The dark photon (also hidden, heavy, para-, or secluded photon) is a hypothetical hidden sector particle, proposed as a force carrier similar to the photon of electromagnetism but potentially connected to dark matter.[1] In a minimal scenario, this new force can be introduced by extending the gauge group of the Standard Model of Particle Physics with a new abelian U(1) gauge symmetry. The corresponding new spin-1 gauge boson (i.e., the dark photon) can then couple very weakly to electrically charged particles through kinetic mixing with the ordinary photon[2] and could thus be detected. The dark photon can also interact with the Standard Model if some of the fermions are charged under the new abelian group. [3] The possible charging arrangements are restricted by a number of consistency requirements such as anomaly cancellation and constraints coming from Yukawa matrices.

Motivation

Observations of gravitational effects, that cannot be explained by visible matter alone, imply the existence of matter which does not or does only very weakly couple to the known forces of Nature. This dark matter dominates the matter density of the Universe, but its particles (if there are any) have eluded direct and indirect detection so far. Given the rich interaction structure of the well-known Standard Model particles, which make up only the subdominant component of the Universe, it is natural to think about a similarly interactive behaviour of dark sector particles. Dark photons could be part of these interactions among dark matter particles and provide a non-gravitational window (a so-called vector portal) into their existence by kinematically mixing with the Standard Model photon.[1][4] Further motivation for the search for dark photons comes from several observed anomalies in astrophysics (e.g. in cosmic rays) that could be related to dark matter interacting with a dark photon.[5][6] Arguably the most interesting application of dark photons arises in the explanation of the discrepancy between the measured and the calculated anomalous magnetic moment of the muon.[7][8][9] This discrepancy is usually thought of as a persisting hint for physics beyond the Standard Model and should be accounted for by general new physics models. Beside the effect on electromagnetism via kinetic mixing and possible interactions with dark matter particles, dark photons (if massive) can also play the role of a dark matter candidate themselves. This is theoretically possible through the misalignment mechanism.[10]

Theory

Adding a sector containing dark photons to the Lagrangian of the Standard Model can be done in a straightforward and minimal way by introducing a new U(1) gauge field.[2] The specifics of the interaction between this new field, potential new particle content (e.g., a Dirac fermion for dark matter) and the Standard Model particles are virtually only limited by the creativity of the theorist and the constraints that have already been put on certain kinds of couplings. The arguably most popular basic model involves a single new broken U(1) gauge symmetry and kinetic mixing between the corresponding dark photon field \( {\displaystyle A^{\prime }} \) and the Standard Model hypercharge fields. The operator at play is \( {\displaystyle F_{\mu \nu }^{\prime }B^{\mu \nu }} \) , where \( {\displaystyle F_{\mu \nu }^{\prime }} is the field strength tensor of the dark photon field and \( {\displaystyle B^{\mu \nu }} \) denotes the field strength tensor of the Standard Model weak hypercharge fields. This term arises naturally by writing down all terms allowed by the gauge symmetry. After electroweak symmetry breaking and diagonalising the terms containing the field strength tensors (kinetic terms) by redefining the fields, the relevant terms in the Lagrangian are

\( {\displaystyle {\mathcal {L}}\supset -{\frac {1}{4}}F^{\prime \mu \nu }F_{\mu \nu }^{\prime }+{\frac {1}{2}}m_{A^{\prime }}^{2}A^{\prime \mu }A_{\mu }^{\prime }+\epsilon eA^{\prime \mu }J_{\mu }^{EM}} \)

where \( {\displaystyle m_{A^{\prime }}} \) is the mass of the dark photon (in this case it can be thought of as being generated by the Higgs or Stueckelberg mechanism), \( \epsilon \) is the parameter describing the kinetic mixing strength and \( {\displaystyle J_{\mu }^{EM}} \) denotes the electromagnetic current with its coupling e. The fundamental parameters of this model are thus the mass of the dark photon and the strength of the kinetic mixing. Other models leave the new U(1) gauge symmetry unbroken, resulting in a massless dark photon carrying a long-range interaction.[11][12] A massless dark photon, however, will experimentally be hard to distinguish from the Standard Model photon. The incorporation of new Dirac fermions as dark matter particles in this theory is uncomplicated and can be achieved by simply adding the Dirac terms to the Lagrangian.[13]

See also

Dark radiation – A postulated type of radiation that mediates interactions of dark matter

Fifth force – Speculative fifth fundamental force

Dual photon – A hypothetical elementary particle that is a dual of the photon under electric–magnetic duality

Photino – Hypothetical superpartner of the photon

References

Essig, R.; Jaros, J. A.; Wester, W.; Adrian, P. Hansson; Andreas, S.; Averett, T.; Baker, O.; Batell, B.; Battaglieri, M. (2013-10-31). "Dark Sectors and New, Light, Weakly-Coupled Particles". arXiv:1311.0029 [hep-ph].

Holdom, Bob (1986-01-09). "Two U(1)'s and ϵ charge shifts". Physics Letters B. 166 (2): 196–198. Bibcode:1986PhLB..166..196H. doi:10.1016/0370-2693(86)91377-8. ISSN 0370-2693.

Galison, Peter; Manohar, Aneesh (1984-03-08). "Two Z's or not two Z's?". Physics Letters B. 136 (4): 279–283. Bibcode:1984PhLB..136..279G. doi:10.1016/0370-2693(84)91161-4. ISSN 0370-2693.

Battaglieri, Marco; Belloni, Alberto; Chou, Aaron; Cushman, Priscilla; Echenard, Bertrand; Essig, Rouven; Estrada, Juan; Feng, Jonathan L.; Flaugher, Brenna (2017-07-14). "US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report". arXiv:1707.04591 [hep-ph].

Pospelov, Maxim; Ritz, Adam (January 2009). "Astrophysical Signatures of Secluded Dark Matter". Physics Letters B. 671 (3): 391–397. arXiv:0810.1502. Bibcode:2009PhLB..671..391P. doi:10.1016/j.physletb.2008.12.012.

Arkani-Hamed, Nima; Finkbeiner, Douglas P.; Slatyer, Tracy R.; Weiner, Neal (2009-01-27). "A Theory of Dark Matter". Physical Review D. 79 (1): 015014. arXiv:0810.0713. Bibcode:2009PhRvD..79a5014A. doi:10.1103/PhysRevD.79.015014. ISSN 1550-7998.

Pospelov, Maxim (2009-11-02). "Secluded U(1) below the weak scale". Physical Review D. 80 (9): 095002. arXiv:0811.1030. Bibcode:2009PhRvD..80i5002P. doi:10.1103/PhysRevD.80.095002. ISSN 1550-7998.

Endo, Motoi; Hamaguchi, Koichi; Mishima, Go (2012-11-27). "Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy". Physical Review D. 86 (9): 095029. arXiv:1209.2558. Bibcode:2012PhRvD..86i5029E. doi:10.1103/PhysRevD.86.095029. ISSN 1550-7998.

Giusti, D.; Lubicz, V.; Martinelli, G.; Sanfilippo, F.; Simula, S. (October 2017). "Strange and charm HVP contributions to the muon ($g - 2)$ including QED corrections with twisted-mass fermions". Journal of High Energy Physics. 2017 (10): 157. arXiv:1707.03019. Bibcode:2017JHEP...10..157G. doi:10.1007/JHEP10(2017)157. ISSN 1029-8479.

Arias, Paola; Cadamuro, Davide; Goodsell, Mark; Jaeckel, Joerg; Redondo, Javier; Ringwald, Andreas (2012-06-08). "WISPy Cold Dark Matter". Journal of Cosmology and Astroparticle Physics. 2012 (6): 013.arXiv:1201.5902. Bibcode:2012JCAP...06..013A. doi:10.1088/1475-7516/2012/06/013. ISSN 1475-7516.

Ackerman, Lotty; Buckley, Matthew R.; Carroll, Sean M.; Kamionkowski, Marc (2009-01-23). "Dark Matter and Dark Radiation". Physical Review D. 79 (2): 023519.arXiv:0810.5126. Bibcode:2009PhRvD..79b3519A. doi:10.1103/PhysRevD.79.023519. ISSN 1550-7998.

Foot, Robert; Vagnozzi, Sunny (2014). "Dissipative hidden sector dark matter". Physical Review D. 91 (2): 023512. arXiv:1409.7174. Bibcode:2015PhRvD..91b3512F. doi:10.1103/PhysRevD.91.023512.

Ilten, Philip; Soreq, Yotam; Williams, Mike; Xue, Wei (2018-01-15). "Serendipity in dark photon searches". Journal of High Energy Physics. 2018 (6): 4. arXiv:1801.04847. Bibcode:2018JHEP...06..004I. doi:10.1007/JHEP06(2018)004.

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Dark matter

Forms of

dark matter

Baryonic dark matter Cold dark matter Hot dark matter Light dark matter Mixed dark matter Warm dark matter Self-interacting dark matter Scalar field dark matter Primordial black holes

Hypothetical particles

Axino Axion Dark photon Holeum LSP Minicharged particle Neutralino Sterile neutrino SIMP WIMP

Theories

and objects

Cuspy halo problem Dark fluid Dark galaxy Dark globular cluster Dark matter halo Dark radiation Dark star Dwarf galaxy problem Halo mass function Mass dimension one fermions Massive compact halo object Mirror matter Navarro–Frenk–White profile Scalar field dark matter

Search

experiments

Direct

detection

ADMX ANAIS ArDM CDEX CDMS CLEAN CoGeNT COSINE COUPP CRESST CUORE D3 DAMA/LIBRA DAMA/NaI DAMIC DarkSide DARWIN DEAP DM-Ice DMTPC DRIFT EDELWEISS EURECA KIMS LUX LZ MACRO MIMAC NAIAD NEWAGE NEWS-G PandaX PICASSO PICO ROSEBUD SABRE SIMPLE TREX-DM UKDMC WARP XENON XMASS ZEPLIN

Indirect

detection

AMS-02 ANTARES ATIC CALET CAST DAMPE Fermi HAWC HESS IceCube MAGIC MOA OGLE PAMELA VERITAS

Other projects

Potential dark galaxies

HE0450-2958 HVC 127-41-330 Smith's Cloud VIRGOHI21

Related

Antimatter Dark energy Exotic matter Galaxy formation and evolution Illustris project Imaginary mass Negative mass UniverseMachine

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Standard Model

Background

Particle physics

Fermions Gauge boson Higgs boson Quantum field theory Gauge theory Strong interaction

Color charge Quantum chromodynamics Quark model Electroweak interaction

Weak interaction Quantum electrodynamics Fermi's interaction Weak hypercharge Weak isospin

Constituents

CKM matrix Spontaneous symmetry breaking Higgs mechanism Mathematical formulation of the Standard Model

Beyond the

Standard Model

Evidence

Hierarchy problem Dark matter Cosmological constant problem Strong CP problem Neutrino oscillation

Theories

Technicolor Kaluza–Klein theory Grand Unified Theory Theory of everything

MSSM Superstring theory Supergravity

String theory Loop quantum gravity Causal dynamical triangulation Canonical quantum gravity Superfluid vacuum theory Twistor theory

Experiments

Gran Sasso INO LHC SNO Super-K Tevatron

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