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Supersymmetry

Supersymmetry is a theoretical framework in physics that suggests the existence of a symmetry between particles with integer spin (bosons) and particles with half-integer spin (fermions). It proposes that for every known particle, there exists a partner particle with different spin properties.[1] There have been multiple experiments on supersymmetry that have failed to provide evidence that it exists in nature.[2] If evidence is found, supersymmetry could help explain certain phenomena, such as the nature of dark matter and the hierarchy problem in particle physics.

A supersymmetric theory is a theory in which the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories exist.[3] In theory, supersymmetry is a type of spacetime symmetry between two basic classes of particles: bosons, which have an integer-valued spin and follow Bose–Einstein statistics, and fermions, which have a half-integer-valued spin and follow Fermi–Dirac statistics.[4]

In supersymmetry, each particle from the class of fermions would have an associated particle in the class of bosons, and vice versa, known as a superpartner. The spin of a particle's superpartner is different by a half-integer. For example, if the electron exists in a supersymmetric theory, then there would be a particle called a selectron (superpartner electron), a bosonic partner of the electron. In the simplest supersymmetry theories, with perfectly "unbroken" supersymmetry, each pair of superpartners would share the same mass and internal quantum numbers besides spin. More complex supersymmetry theories have a spontaneously broken symmetry, allowing superpartners to differ in mass.[5][6][7]

Supersymmetry has various applications to different areas of physics, such as quantum mechanics, statistical mechanics, quantum field theory, condensed matter physics, nuclear physics, optics, stochastic dynamics, astrophysics, quantum gravity, and cosmology. Supersymmetry has also been applied to high energy physics, where a supersymmetric extension of the Standard Model is a possible candidate for physics beyond the Standard Model. However, no supersymmetric extensions of the Standard Model have been experimentally verified.[8][2]

History edit

A supersymmetry relating mesons and baryons was first proposed, in the context of hadronic physics, by Hironari Miyazawa in 1966. This supersymmetry did not involve spacetime, that is, it concerned internal symmetry, and was broken badly. Miyazawa's work was largely ignored at the time.[9][10][11][12]

J. L. Gervais and B. Sakita (in 1971),[13] Yu. A. Golfand and E. P. Likhtman (also in 1971), and D. V. Volkov and V. P. Akulov (1972),[14][15][16] independently rediscovered supersymmetry in the context of quantum field theory, a radically new type of symmetry of spacetime and fundamental fields, which establishes a relationship between elementary particles of different quantum nature, bosons and fermions, and unifies spacetime and internal symmetries of microscopic phenomena. Supersymmetry with a consistent Lie-algebraic graded structure on which the Gervais−Sakita rediscovery was based directly first arose in 1971 in the context of an early version of string theory by Pierre Ramond, John H. Schwarz and André Neveu.[17][18]

In 1974, Julius Wess and Bruno Zumino[19] identified the characteristic renormalization features of four-dimensional supersymmetric field theories, which identified them as remarkable QFTs, and they and Abdus Salam and their fellow researchers introduced early particle physics applications. The mathematical structure of supersymmetry (graded Lie superalgebras) has subsequently been applied successfully to other topics of physics, ranging from nuclear physics,[20][21] critical phenomena,[22] quantum mechanics to statistical physics, and supersymmetry remains a vital part of many proposed theories in many branches of physics.

In particle physics, the first realistic supersymmetric version of the Standard Model was proposed in 1977 by Pierre Fayet and is known as the Minimal Supersymmetric Standard Model or MSSM for short. It was proposed to solve, amongst other things, the hierarchy problem.

Supersymmetry was coined by Abdus Salam and John Strathdee in 1974 as a simplification of the term super-gauge symmetry used by Wess and Zumino.[23] The term supergauge was in turn coined by Neveu and Schwarz in 1971 when they devised supersymmetry in the context of string theory.[18][24]

Applications edit

Extension of possible symmetry groups edit

One reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetries of quantum field theory. These symmetries are grouped into the Poincaré group and internal symmetries and the Coleman–Mandula theorem showed that under certain assumptions, the symmetries of the S-matrix must be a direct product of the Poincaré group with a compact internal symmetry group or if there is not any mass gap, the conformal group with a compact internal symmetry group. In 1971 Golfand and Likhtman were the first to show that the Poincaré algebra can be extended through introduction of four anticommuting spinor generators (in four dimensions), which later became known as supercharges. In 1975, the Haag–Łopuszański–Sohnius theorem analyzed all possible superalgebras in the general form, including those with an extended number of the supergenerators and central charges. This extended super-Poincaré algebra paved the way for obtaining a very large and important class of supersymmetric field theories.

The supersymmetry algebra edit

Traditional symmetries of physics are generated by objects that transform by the tensor representations of the Poincaré group and internal symmetries. Supersymmetries, however, are generated by objects that transform by the spin representations. According to the spin-statistics theorem, bosonic fields commute while fermionic fields anticommute. Combining the two kinds of fields into a single algebra requires the introduction of a Z2-grading under which the bosons are the even elements and the fermions are the odd elements. Such an algebra is called a Lie superalgebra.

The simplest supersymmetric extension of the Poincaré algebra is the Super-Poincaré algebra. Expressed in terms of two Weyl spinors, has the following anti-commutation relation:

 

and all other anti-commutation relations between the Qs and commutation relations between the Qs and Ps vanish. In the above expression Pμ = −iμ are the generators of translation and σμ are the Pauli matrices.

There are representations of a Lie superalgebra that are analogous to representations of a Lie algebra. Each Lie algebra has an associated Lie group and a Lie superalgebra can sometimes be extended into representations of a Lie supergroup.

Supersymmetric quantum mechanics edit

Supersymmetric quantum mechanics adds the SUSY superalgebra to quantum mechanics as opposed to quantum field theory. Supersymmetric quantum mechanics often becomes relevant when studying the dynamics of supersymmetric solitons, and due to the simplified nature of having fields which are only functions of time (rather than space-time), a great deal of progress has been made in this subject and it is now studied in its own right.

SUSY quantum mechanics involves pairs of Hamiltonians which share a particular mathematical relationship, which are called partner Hamiltonians. (The potential energy terms which occur in the Hamiltonians are then known as partner potentials.) An introductory theorem shows that for every eigenstate of one Hamiltonian, its partner Hamiltonian has a corresponding eigenstate with the same energy. This fact can be exploited to deduce many properties of the eigenstate spectrum. It is analogous to the original description of SUSY, which referred to bosons and fermions. We can imagine a "bosonic Hamiltonian", whose eigenstates are the various bosons of our theory. The SUSY partner of this Hamiltonian would be "fermionic", and its eigenstates would be the theory's fermions. Each boson would have a fermionic partner of equal energy.

In finance edit

In 2021, supersymmetric quantum mechanics was applied to option pricing and the analysis of markets in finance,[25] and to financial networks.[26]

Supersymmetry in quantum field theory edit

In quantum field theory, supersymmetry is motivated by solutions to several theoretical problems, for generally providing many desirable mathematical properties, and for ensuring sensible behavior at high energies. Supersymmetric quantum field theory is often much easier to analyze, as many more problems become mathematically tractable. When supersymmetry is imposed as a local symmetry, Einstein's theory of general relativity is included automatically, and the result is said to be a theory of supergravity. Another theoretically appealing property of supersymmetry is that it offers the only "loophole" to the Coleman–Mandula theorem, which prohibits spacetime and internal symmetries from being combined in any nontrivial way, for quantum field theories with very general assumptions. The Haag–Łopuszański–Sohnius theorem demonstrates that supersymmetry is the only way spacetime and internal symmetries can be combined consistently.[27]

While supersymmetry has not been discovered at high energy, see Section Supersymmetry in particle physics, supersymmetry was found to be effectively realized at the intermediate energy of hadronic physics where baryons and mesons are superpartners. An exception is the pion that appears as a zero mode in the mass spectrum and thus protected by the supersymmetry: It has no baryonic partner.[28][29] The realization of this effective supersymmetry is readily explained in quark–diquark models: Because two different color charges close together (e.g., blue and red) appear under coarse resolution as the corresponding anti-color (e.g. anti-green), a diquark cluster viewed with coarse resolution (i.e., at the energy-momentum scale used to study hadron structure) effectively appears as an antiquark. Therefore, a baryon containing 3 valence quarks, of which two tend to cluster together as a diquark, behaves likes a meson.

Supersymmetry in condensed matter physics edit

SUSY concepts have provided useful extensions to the WKB approximation. Additionally, SUSY has been applied to disorder averaged systems both quantum and non-quantum (through statistical mechanics), the Fokker–Planck equation being an example of a non-quantum theory. The 'supersymmetry' in all these systems arises from the fact that one is modelling one particle and as such the 'statistics' do not matter. The use of the supersymmetry method provides a mathematical rigorous alternative to the replica trick, but only in non-interacting systems, which attempts to address the so-called 'problem of the denominator' under disorder averaging. For more on the applications of supersymmetry in condensed matter physics see Efetov (1997).[30]

In 2021, a group of researchers showed that, in theory,   SUSY could be realised at the edge of a Moore–Read quantum Hall state.[31] However, to date, no experiments have been done yet to realise it at an edge of a Moore–Read state. In 2022, a different group of researchers created a computer simulation of atoms in 1 dimensions that had supersymmetric topological quasiparticles.[32]

Supersymmetry in optics edit

In 2013, integrated optics was found[33] to provide a fertile ground on which certain ramifications of SUSY can be explored in readily-accessible laboratory settings. Making use of the analogous mathematical structure of the quantum-mechanical Schrödinger equation and the wave equation governing the evolution of light in one-dimensional settings, one may interpret the refractive index distribution of a structure as a potential landscape in which optical wave packets propagate. In this manner, a new class of functional optical structures with possible applications in phase matching, mode conversion[34] and space-division multiplexing becomes possible. SUSY transformations have been also proposed as a way to address inverse scattering problems in optics and as a one-dimensional transformation optics.[35]

Supersymmetry in dynamical systems edit

All stochastic (partial) differential equations, the models for all types of continuous time dynamical systems, possess topological supersymmetry.[36][37] In the operator representation of stochastic evolution, the topological supersymmetry is the exterior derivative which is commutative with the stochastic evolution operator defined as the stochastically averaged pullback induced on differential forms by SDE-defined diffeomorphisms of the phase space. The topological sector of the so-emerging supersymmetric theory of stochastic dynamics can be recognized as the Witten-type topological field theory.

The meaning of the topological supersymmetry in dynamical systems is the preservation of the phase space continuity—infinitely close points will remain close during continuous time evolution even in the presence of noise. When the topological supersymmetry is broken spontaneously, this property is violated in the limit of the infinitely long temporal evolution and the model can be said to exhibit (the stochastic generalization of) the butterfly effect. From a more general perspective, spontaneous breakdown of the topological supersymmetry is the theoretical essence of the ubiquitous dynamical phenomenon variously known as chaos, turbulence, self-organized criticality etc. The Goldstone theorem explains the associated emergence of the long-range dynamical behavior that manifests itself as 1/f noise, butterfly effect, and the scale-free statistics of sudden (instantonic) processes, such as earthquakes, neuroavalanches, and solar flares, known as the Zipf's law and the Richter scale.

Supersymmetry in mathematics edit

SUSY is also sometimes studied mathematically for its intrinsic properties. This is because it describes complex fields satisfying a property known as holomorphy, which allows holomorphic quantities to be exactly computed. This makes supersymmetric models useful "toy models" of more realistic theories. A prime example of this has been the demonstration of S-duality in four-dimensional gauge theories[38] that interchanges particles and monopoles.

The proof of the Atiyah–Singer index theorem is much simplified by the use of supersymmetric quantum mechanics.

Supersymmetry in string theory edit

Supersymmetry is an integral part of string theory, a possible theory of everything. There are two types of string theory, supersymmetric string theory or superstring theory, and non-supersymmetric string theory. By definition of superstring theory, supersymmetry is required in superstring theory at some level. However, even in non-supersymmetric string theory, a type of supersymmetry called misaligned supersymmetry is still required in the theory in order to ensure no physical tachyons appear.[39][40] Any string theories without some kind of supersymmetry, such as bosonic string theory and the  ,  , and   heterotic string theories, will have a tachyon and therefore the spacetime vacuum itself would be unstable and would decay into some tachyon-free string theory usually in a lower spacetime dimension.[41] There is no experimental evidence that either supersymmetry or misaligned supersymmetry holds in our universe, and many physicists have moved on from supersymmetry and string theory entirely due to the non-detection of supersymmetry at the LHC.[42][43]

Despite the null results for supersymmetry at the LHC so far, some particle physicists have nevertheless moved to string theory in order to resolve the naturalness crisis for certain supersymmetric extensions of the Standard Model.[44] According to the particle physicists, there exists a concept of "stringy naturalness" in string theory,[45] where the string theory landscape could have a power law statistical pull on soft SUSY breaking terms to large values (depending on the number of hidden sector SUSY breaking fields contributing to the soft terms).[46] If this is coupled with an anthropic requirement that contributions to the weak scale not exceed a factor between 2 and 5 from its measured value (as argued by Agrawal et al.),[47] then the Higgs mass is pulled up to the vicinity of 125 GeV while most sparticles are pulled to values beyond the current reach of LHC.[48] An exception occurs for higgsinos which gain mass not from SUSY breaking but rather from whatever mechanism solves the SUSY mu problem. Light higgsino pair production in association with hard initial state jet radiation leads to a soft opposite-sign dilepton plus jet plus missing transverse energy signal.[49]

Supersymmetry in particle physics edit

In particle physics, a supersymmetric extension of the Standard Model is a possible candidate for undiscovered particle physics, and seen by some physicists as an elegant solution to many current problems in particle physics if confirmed correct, which could resolve various areas where current theories are believed to be incomplete and where limitations of current theories are well established.[50][51] In particular, one supersymmetric extension of the Standard Model, the Minimal Supersymmetric Standard Model (MSSM), became popular in theoretical particle physics, as the Minimal Supersymmetric Standard Model is the simplest supersymmetric extension of the Standard Model that could resolve major hierarchy problems within the Standard Model, by guaranteeing that quadratic divergences of all orders will cancel out in perturbation theory. If a supersymmetric extension of the Standard Model is correct, superpartners of the existing elementary particles would be new and undiscovered particles and supersymmetry is expected to be spontaneously broken.

There is no experimental evidence that a supersymmetric extension to the Standard Model is correct, or whether or not other extensions to current models might be more accurate. It is only since around 2010 that particle accelerators specifically designed to study physics beyond the Standard Model have become operational (i.e. the Large Hadron Collider (LHC)), and it is not known where exactly to look, nor the energies required for a successful search. However, the negative results from the LHC since 2010 have already ruled out some supersymmetric extensions to the Standard Model, and many physicists believe that the Minimal Supersymmetric Standard Model, while not ruled out, is no longer able to fully resolve the hierarchy problem.[52]

Supersymmetric extensions of the Standard Model edit

Incorporating supersymmetry into the Standard Model requires doubling the number of particles since there is no way that any of the particles in the Standard Model can be superpartners of each other. With the addition of new particles, there are many possible new interactions. The simplest possible supersymmetric model consistent with the Standard Model is the Minimal Supersymmetric Standard Model (MSSM) which can include the necessary additional new particles that are able to be superpartners of those in the Standard Model.

 
Cancellation of the Higgs boson quadratic mass renormalization between fermionic top quark loop and scalar stop squark tadpole Feynman diagrams in a supersymmetric extension of the Standard Model

One of the original motivations for the Minimal Supersymmetric Standard Model came from the hierarchy problem. Due to the quadratically divergent contributions to the Higgs mass squared in the Standard Model, the quantum mechanical interactions of the Higgs boson causes a large renormalization of the Higgs mass and unless there is an accidental cancellation, the natural size of the Higgs mass is the greatest scale possible. Furthermore, the electroweak scale receives enormous Planck-scale quantum corrections. The observed hierarchy between the electroweak scale and the Planck scale must be achieved with extraordinary fine tuning. This problem is known as the hierarchy problem.

Supersymmetry close to the electroweak scale, such as in the Minimal Supersymmetric Standard Model, would solve the hierarchy problem that afflicts the Standard Model.[53] It would reduce the size of the quantum corrections by having automatic cancellations between fermionic and bosonic Higgs interactions, and Planck-scale quantum corrections cancel between partners and superpartners (owing to a minus sign associated with fermionic loops). The hierarchy between the electroweak scale and the Planck scale would be achieved in a natural manner, without extraordinary fine-tuning. If supersymmetry were restored at the weak scale, then the Higgs mass would be related to supersymmetry breaking which can be induced from small non-perturbative effects explaining the vastly different scales in the weak interactions and gravitational interactions.

Another motivation for the Minimal Supersymmetric Standard Model comes from grand unification, the idea that the gauge symmetry groups should unify at high-energy. In the Standard Model, however, the weak, strong and electromagnetic gauge couplings fail to unify at high energy. In particular, the renormalization group evolution of the three gauge coupling constants of the Standard Model is somewhat sensitive to the present particle content of the theory. These coupling constants do not quite meet together at a common energy scale if we run the renormalization group using the Standard Model.[54][55] After incorporating minimal SUSY at the electroweak scale, the running of the gauge couplings are modified, and joint convergence of the gauge coupling constants is projected to occur at approximately 1016 GeV.[54] The modified running also provides a natural mechanism for radiative electroweak symmetry breaking.

In many supersymmetric extensions of the Standard Model, such as the Minimal Supersymmetric Standard Model, there is a heavy stable particle (such as the neutralino) which could serve as a weakly interacting massive particle (WIMP) dark matter candidate. The existence of a supersymmetric dark matter candidate is related closely to R-parity. Supersymmetry at the electroweak scale (augmented with a discrete symmetry) typically provides a candidate dark matter particle at a mass scale consistent with thermal relic abundance calculations.[56][57]

The standard paradigm for incorporating supersymmetry into a realistic theory is to have the underlying dynamics of the theory be supersymmetric, but the ground state of the theory does not respect the symmetry and supersymmetry is broken spontaneously. The supersymmetry break can not be done permanently by the particles of the MSSM as they currently appear. This means that there is a new sector of the theory that is responsible for the breaking. The only constraint on this new sector is that it must break supersymmetry permanently and must give superparticles TeV scale masses. There are many models that can do this and most of their details do not matter. In order to parameterize the relevant features of supersymmetry breaking, arbitrary soft SUSY breaking terms are added to the theory which temporarily break SUSY explicitly but could never arise from a complete theory of supersymmetry breaking.

Searches and constraints for supersymmetry edit

SUSY extensions of the standard model are constrained by a variety of experiments, including measurements of low-energy observables – for example, the anomalous magnetic moment of the muon at Fermilab; the WMAP dark matter density measurement and direct detection experiments – for example, XENON-100 and LUX; and by particle collider experiments, including B-physics, Higgs phenomenology and direct searches for superpartners (sparticles), at the Large Electron–Positron Collider, Tevatron and the LHC. In fact, CERN publicly states that if a supersymmetric model of the Standard Model "is correct, supersymmetric particles should appear in collisions at the LHC."[58]

Historically, the tightest limits were from direct production at colliders. The first mass limits for squarks and gluinos were made at CERN by the UA1 experiment and the UA2 experiment at the Super Proton Synchrotron. LEP later set very strong limits,[59] which in 2006 were extended by the D0 experiment at the Tevatron.[60][61] From 2003-2015, WMAP's and Planck's dark matter density measurements have strongly constrained supersymmetric extensions of the Standard Model, which, if they explain dark matter, have to be tuned to invoke a particular mechanism to sufficiently reduce the neutralino density.

Prior to the beginning of the LHC, in 2009, fits of available data to CMSSM and NUHM1 indicated that squarks and gluinos were most likely to have masses in the 500 to 800 GeV range, though values as high as 2.5 TeV were allowed with low probabilities. Neutralinos and sleptons were expected to be quite light, with the lightest neutralino and the lightest stau most likely to be found between 100 and 150 GeV.[62]

The first runs of the LHC surpassed existing experimental limits from the Large Electron–Positron Collider and Tevatron and partially excluded the aforementioned expected ranges.[63] In 2011–12, the LHC discovered a Higgs boson with a mass of about 125 GeV, and with couplings to fermions and bosons which are consistent with the Standard Model. The MSSM predicts that the mass of the lightest Higgs boson should not be much higher than the mass of the Z boson, and, in the absence of fine tuning (with the supersymmetry breaking scale on the order of 1 TeV), should not exceed 135 GeV.[64] The LHC found no previously-unknown particles other than the Higgs boson which was already suspected to exist as part of the Standard Model, and therefore no evidence for any supersymmetric extension of the Standard Model.[50][51]

Indirect methods include the search for a permanent electric dipole moment (EDM) in the known Standard Model particles, which can arise when the Standard Model particle interacts with the supersymmetric particles. The current best constraint on the electron electric dipole moment put it to be smaller than 10−28 e·cm, equivalent to a sensitivity to new physics at the TeV scale and matching that of the current best particle colliders.[65] A permanent EDM in any fundamental particle points towards time-reversal violating physics, and therefore also CP-symmetry violation via the CPT theorem. Such EDM experiments are also much more scalable than conventional particle accelerators and offer a practical alternative to detecting physics beyond the standard model as accelerator experiments become increasingly costly and complicated to maintain. The current best limit for the electron's EDM has already reached a sensitivity to rule out so called 'naive' versions of supersymmetric extensions of the Standard Model.[66]

Research in the late 2010s and early 2020s from experimental data on the cosmological constant, LIGO noise, and pulsar timing, suggests it's very unlikely that there are any new particles with masses much higher than those which can be found in the standard model or the LHC.[67][68][69] However, this research has also indicated that quantum gravity or perturbative quantum field theory will become strongly coupled before 1 PeV, leading to other new physics in the TeVs.[67]

Current status edit

The negative findings in the experiments disappointed many physicists, who believed that supersymmetric extensions of the Standard Model (and other theories relying upon it) were by far the most promising theories for "new" physics beyond the Standard Model, and had hoped for signs of unexpected results from the experiments.[8][2] In particular, the LHC result seems problematic for the Minimal Supersymmetric Standard Model, as the value of 125 GeV is relatively large for the model and can only be achieved with large radiative loop corrections from top squarks, which many theorists consider to be "unnatural" (see naturalness and fine tuning).[70]

In response to the so-called "naturalness crisis" in the Minimal Supersymmetric Standard Model, some researchers have abandoned naturalness and the original motivation to solve the hierarchy problem naturally with supersymmetry, while other researchers have moved on to other supersymmetric models such as split supersymmetry.[52][71] Still others have moved to string theory as a result of the naturalness crisis.[72][45][46][48] Former enthusiastic supporter Mikhail Shifman went as far as urging the theoretical community to search for new ideas and accept that supersymmetry was a failed theory in particle physics.[73] However, some researchers suggested that this "naturalness" crisis was premature because various calculations were too optimistic about the limits of masses which would allow a supersymmetric extension of the Standard Model as a solution.[74][75]

General supersymmetry edit

Supersymmetry appears in many related contexts of theoretical physics. It is possible to have multiple supersymmetries and also have supersymmetric extra dimensions.

Extended supersymmetry edit

It is possible to have more than one kind of supersymmetry transformation. Theories with more than one supersymmetry transformation are known as extended supersymmetric theories. The more supersymmetry a theory has, the more constrained are the field content and interactions. Typically the number of copies of a supersymmetry is a power of 2 (1, 2, 4, 8...). In four dimensions, a spinor has four degrees of freedom and thus the minimal number of supersymmetry generators is four in four dimensions and having eight copies of supersymmetry means that there are 32 supersymmetry generators.

The maximal number of supersymmetry generators possible is 32. Theories with more than 32 supersymmetry generators automatically have massless fields with spin greater than 2. It is not known how to make massless fields with spin greater than two interact, so the maximal number of supersymmetry generators considered is 32. This is due to the Weinberg–Witten theorem. This corresponds to an N = 8[clarification needed] supersymmetry theory. Theories with 32 supersymmetries automatically have a graviton.

For four dimensions there are the following theories, with the corresponding multiplets[76] (CPT adds a copy, whenever they are not invariant under such symmetry):

N = 1 Chiral multiplet (0, 1/2)
Vector multiplet (1/2, 1)
Gravitino multiplet (1, 3/2)
Graviton multiplet (3/2, 2)
N = 2 Hypermultiplet (−1/2, 02, 1/2)
Vector multiplet (0, 1/22, 1)
Supergravity multiplet (1, 3/22, 2)
N = 4 Vector multiplet (−1, 1/24, 06, 1/24, 1)
Supergravity multiplet (0, 1/24, 16, 3/24, 2)
N = 8 Supergravity multiplet (−2, 3/28, −128, 1/256, 070, 1/256, 128, 3/28, 2)

Supersymmetry in alternate numbers of dimensions edit

It is possible to have supersymmetry in dimensions other than four. Because the properties of spinors change drastically between different dimensions, each dimension has its characteristic. In d dimensions, the size of spinors is approximately 2d/2 or 2(d − 1)/2. Since the maximum number of supersymmetries is 32, the greatest number of dimensions in which a supersymmetric theory can exist is eleven.[citation needed]

Fractional supersymmetry edit

Fractional supersymmetry is a generalization of the notion of supersymmetry in which the minimal positive amount of spin does not have to be 1/2 but can be an arbitrary 1/N for integer value of N. Such a generalization is possible in two or fewer spacetime dimensions.

See also edit

References edit

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Further reading edit

  • Supersymmetry and Supergravity page in String Theory Wiki lists more books and reviews.

Theoretical introductions, free and online edit

  • Arygres, P. (2001), An Introduction to Global Supersymmetry (PDF).
  • Bilal, A. (2001). "Introduction to Supersymmetry". arXiv:hep-th/0101055.
  • Manuel, D. (1996). "An Introduction to Supersymmetry". arXiv:hep-ph/9611409.
  • Cooper, F.; Khare, A.; Sukhatme, U. (1995). "Supersymmetry and quantum mechanics". Physics Reports (Submitted manuscript). 251 (5–6): 267–385. arXiv:hep-th/9405029. Bibcode:1995PhR...251..267C. doi:10.1016/0370-1573(94)00080-M. S2CID 119379742..
  • Lykken, J. D. (1996). "Introduction to Supersymmetry". arXiv:hep-th/9612114.
  • Martin, S. (2011). "A Supersymmetry Primer". Perspectives on Supersymmetry. Advanced Series on Directions in High Energy Physics. Vol. 18. pp. 1–98. arXiv:hep-ph/9709356. doi:10.1142/9789812839657_0001. ISBN 978-981-02-3553-6. S2CID 118973381.
  • Tong, D. (2021), Supersymmetric Field Theory (PDF).

Monographs edit

  • Baer, H., and Tata, X., Weak Scale Supersymmetry, Cambridge University Press, Cambridge, (1999). ISBN 978-0813341194.
  • Binetruy, P., Supersymmetry: Theory, Experiment, and Cosmology, Oxford University Press, Oxford, (2012). ISBN 978-0199652730.
  • Cecotti, S., Supersymmetric Field Theories: Geometric Structures and Dualities, Cambridge University Press, Cambridge, (2015). ISBN 978-1107053816.
  • Drees, M., Godbole, R., and Roy, P., Theory & Phenomenology of Sparticles, World Scientific, Singapore (2005). ISBN 9-810-23739-1.
  • Dreiner, H.K., Haber, H.E., Martin, S.P., From Spinors to Supersymmetry, Cambridge University Press, Cambridge, (2023). ISBN 978-0521800884.
  • Duplij, S., Siegel, W., and Bagger, J.,Concise Encyclopedia of Supersymmetry, Springer, (2003). ISBN 978-1-4020-1338-6.
  • Freud, P.G.O., Introduction to Supersymmetry, Cambridge University Press, Cambridge, (1988). ISBN 978-0521356756.
  • Junker, G., Supersymmetric Methods in Quantum and Statistical Physics, Springer, (2011). ISBN 978-3-540-61591-0.
  • Kane, G.L., Supersymmetry: Unveiling the Ultimate Laws of Nature, Basic Books, New York (2001). ISBN 0-7382-0489-7.
  • Kane, G.L., and Shifman, M., eds. The Supersymmetric World: The Beginnings of the Theory, World Scientific, Singapore (2000). ISBN 981-02-4522-X.
  • Müller-Kirsten, H.J.W., and Wiedemann, A., Introduction to Supersymmetry, 2nd ed., World Scientific, Singapore (2010). ISBN 978-981-4293-41-9.
  • Nath, P., Supersymmetry, Supergravity and Unification, Cambridge University Press, Cambridge, (2016). ISBN 0-521-19702-3.
  • Raby, S., Supersymmetric Grand Unified Theories, Springer, (2017). ISBN 978-3319552538.
  • Tachikawa, Y., N=2 Supersymmetric Dynamics for Pedestrians, Springer, (2014). ISBN 978-3319088211.
  • Terning, J., Modern Supersymmetry: Dynamics and Duality, Oxford University Press, Oxford, (2009). ISBN 978-0199559510.
  • Wegner, F., Supermathematics and its Applications in Statistical Physics, Springer, (2016). ISBN 978-3662491683.
  • Weinberg, S., The Quantum Theory of Fields, Volume 3: Supersymmetry, Cambridge University Press, Cambridge, (1999). ISBN 0-521-66000-9.
  • Wess, J. and Bagger, J., Supersymmetry and Supergravity, Princeton University Press, Princeton, (1992). ISBN 0-691-02530-4.

On experiments edit

  • Bennett GW, et al. (Muon (g−2) Collaboration) (2004). "Measurement of the negative muon anomalous magnetic moment to 0.7 ppm". Physical Review Letters. 92 (16): 161802. arXiv:hep-ex/0401008. Bibcode:2004PhRvL..92p1802B. doi:10.1103/PhysRevLett.92.161802. PMID 15169217. S2CID 3183567.
  • Brookhaven National Laboratory (Jan 8, 2004). New g−2 measurement deviates further from Standard Model. Press Release.
  • Fermi National Accelerator Laboratory (Sept 25, 2006). Fermilab's CDF scientists have discovered the quick-change behavior of the B-sub-s meson. Press Release.

External links edit

  • Supersymmetry – European Organization for Nuclear Research (CERN)
  • The status of supersymmetry – Symmetry Magazine (Fermilab/SLAC), January 12, 2021
  • As Supersymmetry Fails Tests, Physicists Seek New Ideas – Quanta Magazine, November 20, 2012
  • What is Supersymmetry? – Fermilab, May 21, 2013
  • Why Supersymmetry? – Fermilab, May 31, 2013
  • The Standard Model and Supersymmetry – World Science Festival, March 4, 2015
  • SUSY running out of hiding places – BBC, December 11, 2012

supersymmetry, susy, redirects, here, other, uses, susy, disambiguation, episode, american, series, angel, angel, theoretical, framework, physics, that, suggests, existence, symmetry, between, particles, with, integer, spin, bosons, particles, with, half, inte. SUSY redirects here For other uses see Susy disambiguation For the episode of the American TV series Angel see Supersymmetry Angel Supersymmetry is a theoretical framework in physics that suggests the existence of a symmetry between particles with integer spin bosons and particles with half integer spin fermions It proposes that for every known particle there exists a partner particle with different spin properties 1 There have been multiple experiments on supersymmetry that have failed to provide evidence that it exists in nature 2 If evidence is found supersymmetry could help explain certain phenomena such as the nature of dark matter and the hierarchy problem in particle physics A supersymmetric theory is a theory in which the equations for force and the equations for matter are identical In theoretical and mathematical physics any theory with this property has the principle of supersymmetry SUSY Dozens of supersymmetric theories exist 3 In theory supersymmetry is a type of spacetime symmetry between two basic classes of particles bosons which have an integer valued spin and follow Bose Einstein statistics and fermions which have a half integer valued spin and follow Fermi Dirac statistics 4 In supersymmetry each particle from the class of fermions would have an associated particle in the class of bosons and vice versa known as a superpartner The spin of a particle s superpartner is different by a half integer For example if the electron exists in a supersymmetric theory then there would be a particle called a selectron superpartner electron a bosonic partner of the electron In the simplest supersymmetry theories with perfectly unbroken supersymmetry each pair of superpartners would share the same mass and internal quantum numbers besides spin More complex supersymmetry theories have a spontaneously broken symmetry allowing superpartners to differ in mass 5 6 7 Supersymmetry has various applications to different areas of physics such as quantum mechanics statistical mechanics quantum field theory condensed matter physics nuclear physics optics stochastic dynamics astrophysics quantum gravity and cosmology Supersymmetry has also been applied to high energy physics where a supersymmetric extension of the Standard Model is a possible candidate for physics beyond the Standard Model However no supersymmetric extensions of the Standard Model have been experimentally verified 8 2 Contents 1 History 2 Applications 2 1 Extension of possible symmetry groups 2 1 1 The supersymmetry algebra 2 2 Supersymmetric quantum mechanics 2 2 1 In finance 2 3 Supersymmetry in quantum field theory 2 4 Supersymmetry in condensed matter physics 2 5 Supersymmetry in optics 2 6 Supersymmetry in dynamical systems 2 7 Supersymmetry in mathematics 2 8 Supersymmetry in string theory 3 Supersymmetry in particle physics 3 1 Supersymmetric extensions of the Standard Model 3 2 Searches and constraints for supersymmetry 3 3 Current status 4 General supersymmetry 4 1 Extended supersymmetry 4 2 Supersymmetry in alternate numbers of dimensions 4 3 Fractional supersymmetry 5 See also 6 References 7 Further reading 7 1 Theoretical introductions free and online 7 2 Monographs 7 3 On experiments 8 External linksHistory editA supersymmetry relating mesons and baryons was first proposed in the context of hadronic physics by Hironari Miyazawa in 1966 This supersymmetry did not involve spacetime that is it concerned internal symmetry and was broken badly Miyazawa s work was largely ignored at the time 9 10 11 12 J L Gervais and B Sakita in 1971 13 Yu A Golfand and E P Likhtman also in 1971 and D V Volkov and V P Akulov 1972 14 15 16 independently rediscovered supersymmetry in the context of quantum field theory a radically new type of symmetry of spacetime and fundamental fields which establishes a relationship between elementary particles of different quantum nature bosons and fermions and unifies spacetime and internal symmetries of microscopic phenomena Supersymmetry with a consistent Lie algebraic graded structure on which the Gervais Sakita rediscovery was based directly first arose in 1971 in the context of an early version of string theory by Pierre Ramond John H Schwarz and Andre Neveu 17 18 In 1974 Julius Wess and Bruno Zumino 19 identified the characteristic renormalization features of four dimensional supersymmetric field theories which identified them as remarkable QFTs and they and Abdus Salam and their fellow researchers introduced early particle physics applications The mathematical structure of supersymmetry graded Lie superalgebras has subsequently been applied successfully to other topics of physics ranging from nuclear physics 20 21 critical phenomena 22 quantum mechanics to statistical physics and supersymmetry remains a vital part of many proposed theories in many branches of physics In particle physics the first realistic supersymmetric version of the Standard Model was proposed in 1977 by Pierre Fayet and is known as the Minimal Supersymmetric Standard Model or MSSM for short It was proposed to solve amongst other things the hierarchy problem Supersymmetry was coined by Abdus Salam and John Strathdee in 1974 as a simplification of the term super gauge symmetry used by Wess and Zumino 23 The term supergauge was in turn coined by Neveu and Schwarz in 1971 when they devised supersymmetry in the context of string theory 18 24 Applications editExtension of possible symmetry groups edit One reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetries of quantum field theory These symmetries are grouped into the Poincare group and internal symmetries and the Coleman Mandula theorem showed that under certain assumptions the symmetries of the S matrix must be a direct product of the Poincare group with a compact internal symmetry group or if there is not any mass gap the conformal group with a compact internal symmetry group In 1971 Golfand and Likhtman were the first to show that the Poincare algebra can be extended through introduction of four anticommuting spinor generators in four dimensions which later became known as supercharges In 1975 the Haag Lopuszanski Sohnius theorem analyzed all possible superalgebras in the general form including those with an extended number of the supergenerators and central charges This extended super Poincare algebra paved the way for obtaining a very large and important class of supersymmetric field theories The supersymmetry algebra edit Main article Supersymmetry algebra Traditional symmetries of physics are generated by objects that transform by the tensor representations of the Poincare group and internal symmetries Supersymmetries however are generated by objects that transform by the spin representations According to the spin statistics theorem bosonic fields commute while fermionic fields anticommute Combining the two kinds of fields into a single algebra requires the introduction of a Z2 grading under which the bosons are the even elements and the fermions are the odd elements Such an algebra is called a Lie superalgebra The simplest supersymmetric extension of the Poincare algebra is the Super Poincare algebra Expressed in terms of two Weyl spinors has the following anti commutation relation Q a Q b 2 s m a b P m displaystyle Q alpha bar Q dot beta 2 sigma mu alpha dot beta P mu nbsp and all other anti commutation relations between the Qs and commutation relations between the Qs and Ps vanish In the above expression Pm i m are the generators of translation and sm are the Pauli matrices There are representations of a Lie superalgebra that are analogous to representations of a Lie algebra Each Lie algebra has an associated Lie group and a Lie superalgebra can sometimes be extended into representations of a Lie supergroup Supersymmetric quantum mechanics edit Main article Supersymmetric quantum mechanics Supersymmetric quantum mechanics adds the SUSY superalgebra to quantum mechanics as opposed to quantum field theory Supersymmetric quantum mechanics often becomes relevant when studying the dynamics of supersymmetric solitons and due to the simplified nature of having fields which are only functions of time rather than space time a great deal of progress has been made in this subject and it is now studied in its own right SUSY quantum mechanics involves pairs of Hamiltonians which share a particular mathematical relationship which are called partner Hamiltonians The potential energy terms which occur in the Hamiltonians are then known as partner potentials An introductory theorem shows that for every eigenstate of one Hamiltonian its partner Hamiltonian has a corresponding eigenstate with the same energy This fact can be exploited to deduce many properties of the eigenstate spectrum It is analogous to the original description of SUSY which referred to bosons and fermions We can imagine a bosonic Hamiltonian whose eigenstates are the various bosons of our theory The SUSY partner of this Hamiltonian would be fermionic and its eigenstates would be the theory s fermions Each boson would have a fermionic partner of equal energy In finance edit In 2021 supersymmetric quantum mechanics was applied to option pricing and the analysis of markets in finance 25 and to financial networks 26 Supersymmetry in quantum field theory edit In quantum field theory supersymmetry is motivated by solutions to several theoretical problems for generally providing many desirable mathematical properties and for ensuring sensible behavior at high energies Supersymmetric quantum field theory is often much easier to analyze as many more problems become mathematically tractable When supersymmetry is imposed as a local symmetry Einstein s theory of general relativity is included automatically and the result is said to be a theory of supergravity Another theoretically appealing property of supersymmetry is that it offers the only loophole to the Coleman Mandula theorem which prohibits spacetime and internal symmetries from being combined in any nontrivial way for quantum field theories with very general assumptions The Haag Lopuszanski Sohnius theorem demonstrates that supersymmetry is the only way spacetime and internal symmetries can be combined consistently 27 While supersymmetry has not been discovered at high energy see Section Supersymmetry in particle physics supersymmetry was found to be effectively realized at the intermediate energy of hadronic physics where baryons and mesons are superpartners An exception is the pion that appears as a zero mode in the mass spectrum and thus protected by the supersymmetry It has no baryonic partner 28 29 The realization of this effective supersymmetry is readily explained in quark diquark models Because two different color charges close together e g blue and red appear under coarse resolution as the corresponding anti color e g anti green a diquark cluster viewed with coarse resolution i e at the energy momentum scale used to study hadron structure effectively appears as an antiquark Therefore a baryon containing 3 valence quarks of which two tend to cluster together as a diquark behaves likes a meson Supersymmetry in condensed matter physics edit SUSY concepts have provided useful extensions to the WKB approximation Additionally SUSY has been applied to disorder averaged systems both quantum and non quantum through statistical mechanics the Fokker Planck equation being an example of a non quantum theory The supersymmetry in all these systems arises from the fact that one is modelling one particle and as such the statistics do not matter The use of the supersymmetry method provides a mathematical rigorous alternative to the replica trick but only in non interacting systems which attempts to address the so called problem of the denominator under disorder averaging For more on the applications of supersymmetry in condensed matter physics see Efetov 1997 30 In 2021 a group of researchers showed that in theory N 0 1 displaystyle N 0 1 nbsp SUSY could be realised at the edge of a Moore Read quantum Hall state 31 However to date no experiments have been done yet to realise it at an edge of a Moore Read state In 2022 a different group of researchers created a computer simulation of atoms in 1 dimensions that had supersymmetric topological quasiparticles 32 Supersymmetry in optics edit In 2013 integrated optics was found 33 to provide a fertile ground on which certain ramifications of SUSY can be explored in readily accessible laboratory settings Making use of the analogous mathematical structure of the quantum mechanical Schrodinger equation and the wave equation governing the evolution of light in one dimensional settings one may interpret the refractive index distribution of a structure as a potential landscape in which optical wave packets propagate In this manner a new class of functional optical structures with possible applications in phase matching mode conversion 34 and space division multiplexing becomes possible SUSY transformations have been also proposed as a way to address inverse scattering problems in optics and as a one dimensional transformation optics 35 Supersymmetry in dynamical systems edit Main article Supersymmetric theory of stochastic dynamics All stochastic partial differential equations the models for all types of continuous time dynamical systems possess topological supersymmetry 36 37 In the operator representation of stochastic evolution the topological supersymmetry is the exterior derivative which is commutative with the stochastic evolution operator defined as the stochastically averaged pullback induced on differential forms by SDE defined diffeomorphisms of the phase space The topological sector of the so emerging supersymmetric theory of stochastic dynamics can be recognized as the Witten type topological field theory The meaning of the topological supersymmetry in dynamical systems is the preservation of the phase space continuity infinitely close points will remain close during continuous time evolution even in the presence of noise When the topological supersymmetry is broken spontaneously this property is violated in the limit of the infinitely long temporal evolution and the model can be said to exhibit the stochastic generalization of the butterfly effect From a more general perspective spontaneous breakdown of the topological supersymmetry is the theoretical essence of the ubiquitous dynamical phenomenon variously known as chaos turbulence self organized criticality etc The Goldstone theorem explains the associated emergence of the long range dynamical behavior that manifests itself as 1 f noise butterfly effect and the scale free statistics of sudden instantonic processes such as earthquakes neuroavalanches and solar flares known as the Zipf s law and the Richter scale Supersymmetry in mathematics edit SUSY is also sometimes studied mathematically for its intrinsic properties This is because it describes complex fields satisfying a property known as holomorphy which allows holomorphic quantities to be exactly computed This makes supersymmetric models useful toy models of more realistic theories A prime example of this has been the demonstration of S duality in four dimensional gauge theories 38 that interchanges particles and monopoles The proof of the Atiyah Singer index theorem is much simplified by the use of supersymmetric quantum mechanics Supersymmetry in string theory edit Main articles Superstring theory String theory and String theory landscape Supersymmetry is an integral part of string theory a possible theory of everything There are two types of string theory supersymmetric string theory or superstring theory and non supersymmetric string theory By definition of superstring theory supersymmetry is required in superstring theory at some level However even in non supersymmetric string theory a type of supersymmetry called misaligned supersymmetry is still required in the theory in order to ensure no physical tachyons appear 39 40 Any string theories without some kind of supersymmetry such as bosonic string theory and the E 7 E 7 displaystyle E 7 times E 7 nbsp S U 16 displaystyle SU 16 nbsp and E 8 displaystyle E 8 nbsp heterotic string theories will have a tachyon and therefore the spacetime vacuum itself would be unstable and would decay into some tachyon free string theory usually in a lower spacetime dimension 41 There is no experimental evidence that either supersymmetry or misaligned supersymmetry holds in our universe and many physicists have moved on from supersymmetry and string theory entirely due to the non detection of supersymmetry at the LHC 42 43 Despite the null results for supersymmetry at the LHC so far some particle physicists have nevertheless moved to string theory in order to resolve the naturalness crisis for certain supersymmetric extensions of the Standard Model 44 According to the particle physicists there exists a concept of stringy naturalness in string theory 45 where the string theory landscape could have a power law statistical pull on soft SUSY breaking terms to large values depending on the number of hidden sector SUSY breaking fields contributing to the soft terms 46 If this is coupled with an anthropic requirement that contributions to the weak scale not exceed a factor between 2 and 5 from its measured value as argued by Agrawal et al 47 then the Higgs mass is pulled up to the vicinity of 125 GeV while most sparticles are pulled to values beyond the current reach of LHC 48 An exception occurs for higgsinos which gain mass not from SUSY breaking but rather from whatever mechanism solves the SUSY mu problem Light higgsino pair production in association with hard initial state jet radiation leads to a soft opposite sign dilepton plus jet plus missing transverse energy signal 49 Supersymmetry in particle physics editIn particle physics a supersymmetric extension of the Standard Model is a possible candidate for undiscovered particle physics and seen by some physicists as an elegant solution to many current problems in particle physics if confirmed correct which could resolve various areas where current theories are believed to be incomplete and where limitations of current theories are well established 50 51 In particular one supersymmetric extension of the Standard Model the Minimal Supersymmetric Standard Model MSSM became popular in theoretical particle physics as the Minimal Supersymmetric Standard Model is the simplest supersymmetric extension of the Standard Model that could resolve major hierarchy problems within the Standard Model by guaranteeing that quadratic divergences of all orders will cancel out in perturbation theory If a supersymmetric extension of the Standard Model is correct superpartners of the existing elementary particles would be new and undiscovered particles and supersymmetry is expected to be spontaneously broken There is no experimental evidence that a supersymmetric extension to the Standard Model is correct or whether or not other extensions to current models might be more accurate It is only since around 2010 that particle accelerators specifically designed to study physics beyond the Standard Model have become operational i e the Large Hadron Collider LHC and it is not known where exactly to look nor the energies required for a successful search However the negative results from the LHC since 2010 have already ruled out some supersymmetric extensions to the Standard Model and many physicists believe that the Minimal Supersymmetric Standard Model while not ruled out is no longer able to fully resolve the hierarchy problem 52 Supersymmetric extensions of the Standard Model edit Main article Minimal Supersymmetric Standard Model Incorporating supersymmetry into the Standard Model requires doubling the number of particles since there is no way that any of the particles in the Standard Model can be superpartners of each other With the addition of new particles there are many possible new interactions The simplest possible supersymmetric model consistent with the Standard Model is the Minimal Supersymmetric Standard Model MSSM which can include the necessary additional new particles that are able to be superpartners of those in the Standard Model nbsp Cancellation of the Higgs boson quadratic mass renormalization between fermionic top quark loop and scalar stop squark tadpole Feynman diagrams in a supersymmetric extension of the Standard ModelOne of the original motivations for the Minimal Supersymmetric Standard Model came from the hierarchy problem Due to the quadratically divergent contributions to the Higgs mass squared in the Standard Model the quantum mechanical interactions of the Higgs boson causes a large renormalization of the Higgs mass and unless there is an accidental cancellation the natural size of the Higgs mass is the greatest scale possible Furthermore the electroweak scale receives enormous Planck scale quantum corrections The observed hierarchy between the electroweak scale and the Planck scale must be achieved with extraordinary fine tuning This problem is known as the hierarchy problem Supersymmetry close to the electroweak scale such as in the Minimal Supersymmetric Standard Model would solve the hierarchy problem that afflicts the Standard Model 53 It would reduce the size of the quantum corrections by having automatic cancellations between fermionic and bosonic Higgs interactions and Planck scale quantum corrections cancel between partners and superpartners owing to a minus sign associated with fermionic loops The hierarchy between the electroweak scale and the Planck scale would be achieved in a natural manner without extraordinary fine tuning If supersymmetry were restored at the weak scale then the Higgs mass would be related to supersymmetry breaking which can be induced from small non perturbative effects explaining the vastly different scales in the weak interactions and gravitational interactions Another motivation for the Minimal Supersymmetric Standard Model comes from grand unification the idea that the gauge symmetry groups should unify at high energy In the Standard Model however the weak strong and electromagnetic gauge couplings fail to unify at high energy In particular the renormalization group evolution of the three gauge coupling constants of the Standard Model is somewhat sensitive to the present particle content of the theory These coupling constants do not quite meet together at a common energy scale if we run the renormalization group using the Standard Model 54 55 After incorporating minimal SUSY at the electroweak scale the running of the gauge couplings are modified and joint convergence of the gauge coupling constants is projected to occur at approximately 1016 GeV 54 The modified running also provides a natural mechanism for radiative electroweak symmetry breaking In many supersymmetric extensions of the Standard Model such as the Minimal Supersymmetric Standard Model there is a heavy stable particle such as the neutralino which could serve as a weakly interacting massive particle WIMP dark matter candidate The existence of a supersymmetric dark matter candidate is related closely to R parity Supersymmetry at the electroweak scale augmented with a discrete symmetry typically provides a candidate dark matter particle at a mass scale consistent with thermal relic abundance calculations 56 57 The standard paradigm for incorporating supersymmetry into a realistic theory is to have the underlying dynamics of the theory be supersymmetric but the ground state of the theory does not respect the symmetry and supersymmetry is broken spontaneously The supersymmetry break can not be done permanently by the particles of the MSSM as they currently appear This means that there is a new sector of the theory that is responsible for the breaking The only constraint on this new sector is that it must break supersymmetry permanently and must give superparticles TeV scale masses There are many models that can do this and most of their details do not matter In order to parameterize the relevant features of supersymmetry breaking arbitrary soft SUSY breaking terms are added to the theory which temporarily break SUSY explicitly but could never arise from a complete theory of supersymmetry breaking Searches and constraints for supersymmetry edit SUSY extensions of the standard model are constrained by a variety of experiments including measurements of low energy observables for example the anomalous magnetic moment of the muon at Fermilab the WMAP dark matter density measurement and direct detection experiments for example XENON 100 and LUX and by particle collider experiments including B physics Higgs phenomenology and direct searches for superpartners sparticles at the Large Electron Positron Collider Tevatron and the LHC In fact CERN publicly states that if a supersymmetric model of the Standard Model is correct supersymmetric particles should appear in collisions at the LHC 58 Historically the tightest limits were from direct production at colliders The first mass limits for squarks and gluinos were made at CERN by the UA1 experiment and the UA2 experiment at the Super Proton Synchrotron LEP later set very strong limits 59 which in 2006 were extended by the D0 experiment at the Tevatron 60 61 From 2003 2015 WMAP s and Planck s dark matter density measurements have strongly constrained supersymmetric extensions of the Standard Model which if they explain dark matter have to be tuned to invoke a particular mechanism to sufficiently reduce the neutralino density Prior to the beginning of the LHC in 2009 fits of available data to CMSSM and NUHM1 indicated that squarks and gluinos were most likely to have masses in the 500 to 800 GeV range though values as high as 2 5 TeV were allowed with low probabilities Neutralinos and sleptons were expected to be quite light with the lightest neutralino and the lightest stau most likely to be found between 100 and 150 GeV 62 The first runs of the LHC surpassed existing experimental limits from the Large Electron Positron Collider and Tevatron and partially excluded the aforementioned expected ranges 63 In 2011 12 the LHC discovered a Higgs boson with a mass of about 125 GeV and with couplings to fermions and bosons which are consistent with the Standard Model The MSSM predicts that the mass of the lightest Higgs boson should not be much higher than the mass of the Z boson and in the absence of fine tuning with the supersymmetry breaking scale on the order of 1 TeV should not exceed 135 GeV 64 The LHC found no previously unknown particles other than the Higgs boson which was already suspected to exist as part of the Standard Model and therefore no evidence for any supersymmetric extension of the Standard Model 50 51 Indirect methods include the search for a permanent electric dipole moment EDM in the known Standard Model particles which can arise when the Standard Model particle interacts with the supersymmetric particles The current best constraint on the electron electric dipole moment put it to be smaller than 10 28 e cm equivalent to a sensitivity to new physics at the TeV scale and matching that of the current best particle colliders 65 A permanent EDM in any fundamental particle points towards time reversal violating physics and therefore also CP symmetry violation via the CPT theorem Such EDM experiments are also much more scalable than conventional particle accelerators and offer a practical alternative to detecting physics beyond the standard model as accelerator experiments become increasingly costly and complicated to maintain The current best limit for the electron s EDM has already reached a sensitivity to rule out so called naive versions of supersymmetric extensions of the Standard Model 66 Research in the late 2010s and early 2020s from experimental data on the cosmological constant LIGO noise and pulsar timing suggests it s very unlikely that there are any new particles with masses much higher than those which can be found in the standard model or the LHC 67 68 69 However this research has also indicated that quantum gravity or perturbative quantum field theory will become strongly coupled before 1 PeV leading to other new physics in the TeVs 67 Current status edit The negative findings in the experiments disappointed many physicists who believed that supersymmetric extensions of the Standard Model and other theories relying upon it were by far the most promising theories for new physics beyond the Standard Model and had hoped for signs of unexpected results from the experiments 8 2 In particular the LHC result seems problematic for the Minimal Supersymmetric Standard Model as the value of 125 GeV is relatively large for the model and can only be achieved with large radiative loop corrections from top squarks which many theorists consider to be unnatural see naturalness and fine tuning 70 In response to the so called naturalness crisis in the Minimal Supersymmetric Standard Model some researchers have abandoned naturalness and the original motivation to solve the hierarchy problem naturally with supersymmetry while other researchers have moved on to other supersymmetric models such as split supersymmetry 52 71 Still others have moved to string theory as a result of the naturalness crisis 72 45 46 48 Former enthusiastic supporter Mikhail Shifman went as far as urging the theoretical community to search for new ideas and accept that supersymmetry was a failed theory in particle physics 73 However some researchers suggested that this naturalness crisis was premature because various calculations were too optimistic about the limits of masses which would allow a supersymmetric extension of the Standard Model as a solution 74 75 General supersymmetry editSupersymmetry appears in many related contexts of theoretical physics It is possible to have multiple supersymmetries and also have supersymmetric extra dimensions Extended supersymmetry edit It is possible to have more than one kind of supersymmetry transformation Theories with more than one supersymmetry transformation are known as extended supersymmetric theories The more supersymmetry a theory has the more constrained are the field content and interactions Typically the number of copies of a supersymmetry is a power of 2 1 2 4 8 In four dimensions a spinor has four degrees of freedom and thus the minimal number of supersymmetry generators is four in four dimensions and having eight copies of supersymmetry means that there are 32 supersymmetry generators The maximal number of supersymmetry generators possible is 32 Theories with more than 32 supersymmetry generators automatically have massless fields with spin greater than 2 It is not known how to make massless fields with spin greater than two interact so the maximal number of supersymmetry generators considered is 32 This is due to the Weinberg Witten theorem This corresponds to an N 8 clarification needed supersymmetry theory Theories with 32 supersymmetries automatically have a graviton For four dimensions there are the following theories with the corresponding multiplets 76 CPT adds a copy whenever they are not invariant under such symmetry N 1 Chiral multiplet 0 1 2 Vector multiplet 1 2 1 Gravitino multiplet 1 3 2 Graviton multiplet 3 2 2 N 2 Hypermultiplet 1 2 02 1 2 Vector multiplet 0 1 2 2 1 Supergravity multiplet 1 3 2 2 2 N 4 Vector multiplet 1 1 2 4 06 1 2 4 1 Supergravity multiplet 0 1 2 4 16 3 2 4 2 N 8 Supergravity multiplet 2 3 2 8 128 1 2 56 070 1 2 56 128 3 2 8 2 Supersymmetry in alternate numbers of dimensions edit It is possible to have supersymmetry in dimensions other than four Because the properties of spinors change drastically between different dimensions each dimension has its characteristic In d dimensions the size of spinors is approximately 2d 2 or 2 d 1 2 Since the maximum number of supersymmetries is 32 the greatest number of dimensions in which a supersymmetric theory can exist is eleven citation needed Fractional supersymmetry edit Fractional supersymmetry is a generalization of the notion of supersymmetry in which the minimal positive amount of spin does not have to be 1 2 but can be an arbitrary 1 N for integer value of N Such a generalization is possible in two or fewer spacetime dimensions See also editAnyon Next to Minimal Supersymmetric Standard Model Quantum group Split supersymmetry Supercharge Supermultiplet Supergeometry Supergravity Supergroup Superpartner Superspace Supersplit supersymmetry Supersymmetric gauge theory Supersymmetry nonrenormalization theorems Wess Zumino modelReferences edit Supersymmetry CERN Archived from the original on 2023 07 14 Retrieved 2023 09 11 a b c Wolchover Natalie August 9 2016 What No New Particles Means for Physics Quanta Magazine What is Supersymmetry 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University Department of Physics Princeton University Department of Physics p 91 Dienes Keith R 7 November 1994 Modular invariance finiteness and misaligned supersymmetry New constraints on the numbers of physical string states Nuclear Physics B 429 3 533 588 arXiv hep th 9402006 Bibcode 1994NuPhB 429 533D doi 10 1016 0550 3213 94 90153 8 S2CID 14794874 Abel Steven Dienes Keith R Mavroudi Einni 15 June 2015 Towards a Non Supersymmetric String Phenomenology Physical Review D 91 12 126014 arXiv 1502 03087 Bibcode 2015PhRvD 91l6014A doi 10 1103 PhysRevD 91 126014 S2CID 118655927 Kaidi Justin 15 May 2021 Stable Vacua for Tachyonic Strings Physical Review D 103 10 106026 arXiv 2010 10521 Bibcode 2021PhRvD 103j6026K doi 10 1103 PhysRevD 103 106026 S2CID 224814212 Physics seeks the future The Economist 28 August 2021 Retrieved 31 August 2021 Fundamental physics is humanity s most extraordinary achievement The Economist 28 August 2021 Retrieved 31 August 2021 See below at section Supersymmetry Supersymmetry in particle physics for details a b Baer H Barger V Salam S June 2019 Naturalness versus stringy naturalness with implications for collider and dark matter searches Physical Review Research 1 2 023001 arXiv 1906 07741 Bibcode 2019PhRvR 1b3001B doi 10 1103 PhysRevResearch 1 023001 S2CID 195068902 a b Douglas Michael R May 2004 Statistical analysis of the supersymmetry breaking scale arXiv hep th 0405279 Agrawal V Barr S Donoghue J F Seckel D January 1998 Anthropic considerations in multiple domain theories and the scale of electroweak symmetry breaking Physical Review Letters 80 9 1822 1825 arXiv hep ph 9801253 Bibcode 1998PhRvL 80 1822A doi 10 1103 PhysRevLett 80 1822 S2CID 14397884 a b Baer H Barger V Serce H Sinha K December 2017 Higgs and superparticle mass predictions from the landscape Journal of High Energy Physics 1803 3 002 arXiv 1712 01399 doi 10 1007 JHEP03 2018 002 S2CID 113404486 Baer H Mustafayev A Tata X September 2014 Monojet plus soft dilepton signal from light higgsino pair production at LHC14 Physical Review D 90 11 115007 arXiv 1409 7058 Bibcode 2014PhRvD 90k5007B doi 10 1103 PhysRevD 90 115007 S2CID 119194219 a b ATLAS Supersymmetry Public Results ATLAS Collaboration CERN Retrieved 24 September 2017 a b CMS Supersymmetry Public Results CMS CERN Retrieved 24 September 2017 a b Hershberger Scott 12 January 2021 The status of supersymmetry Symmetry Magazine Retrieved 29 June 2021 David Curtin August 2011 Model Building And Collider Physics Above The Weak Scale PDF PhD thesis Cornell University a b Kane Gordon L June 2003 The Dawn of Physics Beyond the Standard Model Scientific American 288 6 68 75 Bibcode 2003SciAm 288f 68K doi 10 1038 scientificamerican0603 68 PMID 12764939 The Frontiers of Physics Scientific American Special ed 15 3 8 2005 Feng Jonathan 11 May 2007 Supersymmetric Dark Matter PDF University of California Irvine Archived from the original PDF on 11 May 2013 Retrieved 16 February 2013 Bringmann Torsten The WIMP Miracle PDF University of Hamburg Archived from the original PDF on 1 March 2013 Supersymmetry predicts a partner particle for each particle in the Standard Model to help explain why particles have mass CERN Supersymmetry Retrieved 5 September 2019 LEP2 SUSY Working Group 2004 ALEPH DELPHI L3 and OPAL experiments charginos large m0 LEPSUSYWG 01 03 1 The D0 Collaboration 2009 Search for associated production of charginos and neutralinos in the trilepton final state using 2 3 fb 1 of data Physics Letters B 680 1 34 43 arXiv 0901 0646 Bibcode 2009PhLB 680 34D doi 10 1016 j physletb 2009 08 011 hdl 10211 3 195394 S2CID 54016374 The D0 Collaboration 2008 Search for squarks and gluinos in events with jets and missing transverse energy using 2 1 fb 1 of pp collision data at s 1 96 TeV Physics Letters B 660 5 449 457 arXiv 0712 3805 Bibcode 2008PhLB 660 449D doi 10 1016 j physletb 2008 01 042 S2CID 18574837 Buchmueller O et al 2009 Likelihood Functions for Supersymmetric Observables in Frequentist 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the Electric Dipole Moment of the Electron PDF Nature 562 7727 355 360 Bibcode 2018Natur 562 355A doi 10 1038 s41586 018 0599 8 PMID 30333583 S2CID 52985540 a b Afshordi Niayesh Nelson Elliot 7 April 2016 Cosmological bounds on TeV scale physics and beyond Physical Review D 93 8 083505 arXiv 1504 00012 Bibcode 2016PhRvD 93h3505A doi 10 1103 PhysRevD 93 083505 S2CID 119110506 Retrieved 20 February 2023 Afshordi Niayesh 21 November 2019 On the origin of the LIGO mystery noise and the high energy particle physics desert arXiv 1911 09384 gr qc Afshordi Niayesh Kim Hyungjin Nelson Elliot 15 March 2017 Pulsar Timing Constraints on Physics Beyond the Standard Model arXiv 1703 05331 hep th Draper Patrick Meade Patrick Reece Matthew Shih David December 2011 Implications of a 125 GeV Higgs for the MSSM and Low Scale SUSY Breaking Physical Review D 85 9 095007 arXiv 1112 3068 Bibcode 2012PhRvD 85i5007D doi 10 1103 PhysRevD 85 095007 S2CID 118577425 Witten reflects CERN Courier 21 December 2021 Retrieved 23 December 2021 See the section Supersymmetry Supersymmetry in string theory above for details Shifman M 31 October 2012 Reflections and Impressionistic Portrait Frontiers Beyond the Standard Model FTPI arXiv 1211 0004v1 Baer Howard Barger Vernon Mickelson Dan September 2013 How conventional measures overestimate electroweak fine tuning in supersymmetric theory Physical Review D 88 9 095013 arXiv 1309 2984 Bibcode 2013PhRvD 88i5013B doi 10 1103 PhysRevD 88 095013 S2CID 119288477 Baer Howard Barger Vernon Huang Peisi Mickelson Dan Mustafayev Azar Tata Xerxes December 2012 Radiative natural supersymmetry Reconciling electroweak fine tuning and the Higgs boson mass Physical Review D 87 11 115028 arXiv 1212 2655 Bibcode 2013PhRvD 87k5028B doi 10 1103 PhysRevD 87 115028 S2CID 73588737 Polchinski J String Theory Vol 2 Superstring theory and beyond Appendix BFurther reading editSupersymmetry and Supergravity page in String Theory Wiki lists more books and reviews Theoretical introductions free and online edit Arygres P 2001 An Introduction to Global Supersymmetry PDF Bilal A 2001 Introduction to Supersymmetry arXiv hep th 0101055 Manuel D 1996 An Introduction to Supersymmetry arXiv hep ph 9611409 Cooper F Khare A Sukhatme U 1995 Supersymmetry and quantum mechanics Physics Reports Submitted manuscript 251 5 6 267 385 arXiv hep th 9405029 Bibcode 1995PhR 251 267C doi 10 1016 0370 1573 94 00080 M S2CID 119379742 Lykken J D 1996 Introduction to Supersymmetry arXiv hep th 9612114 Martin S 2011 A Supersymmetry Primer Perspectives on Supersymmetry Advanced Series on Directions in High Energy Physics Vol 18 pp 1 98 arXiv hep ph 9709356 doi 10 1142 9789812839657 0001 ISBN 978 981 02 3553 6 S2CID 118973381 Tong D 2021 Supersymmetric Field Theory PDF Monographs edit Baer H and Tata X Weak Scale Supersymmetry Cambridge University Press Cambridge 1999 ISBN 978 0813341194 Binetruy P Supersymmetry Theory Experiment and Cosmology Oxford University Press Oxford 2012 ISBN 978 0199652730 Cecotti S Supersymmetric Field Theories Geometric Structures and Dualities Cambridge University Press Cambridge 2015 ISBN 978 1107053816 Drees M Godbole R and Roy P Theory amp Phenomenology of Sparticles World Scientific Singapore 2005 ISBN 9 810 23739 1 Dreiner H K Haber H E Martin S P From Spinors to Supersymmetry Cambridge University Press Cambridge 2023 ISBN 978 0521800884 Duplij S Siegel W and Bagger J Concise Encyclopedia of Supersymmetry Springer 2003 ISBN 978 1 4020 1338 6 Freud P G O Introduction to Supersymmetry Cambridge University Press Cambridge 1988 ISBN 978 0521356756 Junker G Supersymmetric Methods in Quantum and Statistical Physics Springer 2011 ISBN 978 3 540 61591 0 Kane G L Supersymmetry Unveiling the Ultimate Laws of Nature Basic Books New York 2001 ISBN 0 7382 0489 7 Kane G L and Shifman M eds The Supersymmetric World The Beginnings of the Theory World Scientific Singapore 2000 ISBN 981 02 4522 X Muller Kirsten H J W and Wiedemann A Introduction to Supersymmetry 2nd ed World Scientific Singapore 2010 ISBN 978 981 4293 41 9 Nath P Supersymmetry Supergravity and Unification Cambridge University Press Cambridge 2016 ISBN 0 521 19702 3 Raby S Supersymmetric Grand Unified Theories Springer 2017 ISBN 978 3319552538 Tachikawa Y N 2 Supersymmetric Dynamics for Pedestrians Springer 2014 ISBN 978 3319088211 Terning J Modern Supersymmetry Dynamics and Duality Oxford University Press Oxford 2009 ISBN 978 0199559510 Wegner F Supermathematics and its Applications in Statistical Physics Springer 2016 ISBN 978 3662491683 Weinberg S The Quantum Theory of Fields Volume 3 Supersymmetry Cambridge University Press Cambridge 1999 ISBN 0 521 66000 9 Wess J and Bagger J Supersymmetry and Supergravity Princeton University Press Princeton 1992 ISBN 0 691 02530 4 On experiments edit Bennett GW et al Muon g 2 Collaboration 2004 Measurement of the negative muon anomalous magnetic moment to 0 7 ppm Physical Review Letters 92 16 161802 arXiv hep ex 0401008 Bibcode 2004PhRvL 92p1802B doi 10 1103 PhysRevLett 92 161802 PMID 15169217 S2CID 3183567 Brookhaven National Laboratory Jan 8 2004 New g 2 measurement deviates further from Standard Model Press Release Fermi National Accelerator Laboratory Sept 25 2006 Fermilab s CDF scientists have discovered the quick change behavior of the B sub s meson Press Release External links edit nbsp Wikiquote has quotations related to Supersymmetry Supersymmetry European Organization for Nuclear Research CERN The status of supersymmetry Symmetry Magazine Fermilab SLAC January 12 2021 As Supersymmetry Fails Tests Physicists Seek New Ideas Quanta Magazine November 20 2012 What is Supersymmetry Fermilab May 21 2013 Why Supersymmetry Fermilab May 31 2013 The Standard Model and Supersymmetry World Science Festival March 4 2015 SUSY running out of hiding places BBC December 11 2012 Retrieved from https en wikipedia org w index php title Supersymmetry amp oldid 1190109271, wikipedia, wiki, book, books, library,

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