Dark Photon Research Articles

Probing the dark photon via polarized DIS scattering at the HERA and EIC

The dark photon is widely predicted in many new physics beyond the Standard Model. In this work, we propose to utilize the polarized lepton cross section and single-spin asymmetry in neutral current DIS process at the HERA and upcoming Electron-Ion Collider (EIC) to probe the properties of the dark photon. It shows that we can constrain the mixing parameter ϵ<0.02 when the dark photon mass mAD<10GeV at the HERA with polarized lepton beam and this bound is comparable to the limit from the unpolarized data of HERA I and II. With the help of high integrated luminosity and high electron beam polarization of the EIC, the upper limit of the ϵ could be further improved. Depending on the assumption of the systematic error of the cross section measurements, we obtain ϵ<0.01∼0.02 for the mass region mAD<10GeV under the integrated luminosity of 300fb−1. A similar and robust upper limit for the ϵ could be obtained from the single-spin asymmetry measurement, which is not depending on the assumption of the systematic errors.

Implication of the dark axion portal for the EDM of fermions and dark matter probing with NA64e , NA64μ , LDMX, M3 , and BaBar

The link between ordinary Standard Model (SM) photons and both dark photons and axion-like particles (ALPs) can be introduced through the dark axion portal coupling. Given the dark axion portal setup, in the present paper we refer to the dark photon as the mediator between SM and dark matter (DM) particles, implying that it decays predominantly into a pair of DM fermions. Furthermore, we discuss in detail the implication of the dark axion portal scenario for the lepton (electron and muon) fixed-target experiments. In particular, for the specific fixed-target facility we study the missing-energy signatures of the dark photon production followed by its invisible decay into stable DM particles. We investigate the potential to probe dark axion portal vertices with regarding signatures and derive the expected sensitivities of $\mathrm{NA}64e$, $\mathrm{NA}64\ensuremath{\mu}$, LDMX and ${\mathrm{M}}^{3}$. Moreover, we estimate the expected reach of $\mathrm{NA}64e$ from the projected statistics of the $J/\ensuremath{\psi}$ vector meson invisible decays. We also recast the BABAR monophoton bounds for the specific dark axion portal scenario. In addition, we modify the dark axion portal setup by including in the model both the hadron- and lepton-specific ALP couplings. As a result, we obtain the bounds on the combination of fermion-specific couplings of ALP from the fixed-target experiments. We discuss the implication of the modified dark axion portal scenario for the electric dipole moments (EDMs) of SM fermions. In addition, we derive novel constraints on the combination of the $CP$-violating neutron-specific ALP couplings from the existing bounds on neutron EDMs by taking into account the neutron anomalous magnetic moment.

Fingerprints of freeze-in dark matter in an early matter-dominated era

We study the impact of an alternate cosmological history with an early matter-dominated epoch on the freeze-in production of dark matter. Such early matter domination is triggered by a meta-stable matter field dissipating into radiation. In general, the dissipation rate has a non-trivial temperature and scale factor dependence. Compared to the usual case of dark matter production via the freeze-in mechanism in a radiation-dominated universe, in this scenario, orders of magnitude larger coupling between the visible and the dark sector can be accommodated. Finally, as a proof of principle, we consider a specific model where the dark matter is produced by a sub-GeV dark photon having a kinetic mixing with the Standard Model photon. We point out that the parameter space of this model can be probed by the experiments in the presence of an early matter-dominated era.

Hitting two BSM particles with one lepton-jet: search for a top partner decaying to a dark photon, resulting in a lepton-jet

A maverick top partner model, decaying to a dark photon was suggested in Ref. [1]. The dark photon decays to two overlapping electrons for dark photon masses of \approx 100≈100 MeV, and results in a so-called lepton-jet. The event includes a top quark as well, which results in events with two boosted objects, one heavy and the other light. We propose a search strategy exploiting the unique signal topology. We show that for a set of kinematic selections, both in hadronic and leptonic decay channel of the SM top quark, almost all background can be eliminated, leaving enough signal events up to top partner mass of about 3.5 TeV for the search to be viable at the LHC Run 2. Further, integrated luminosity needed for the proposed search to be sensitive is presented as a function of top partner mass.

Einstein–Cartan–Holst–Proca dynamos massive photons as dark matter and GWs

In this paper, we extend Shaposhnikov et al.'s parity violating the Einstein–Cartan–Holst action by adding to Holst term H, a Proca photon–torsion coupling χpt = 10−24 as computed by De Sabbata, Garcia de Andrade, and Sivaram. The strength of Holst term is obtained, in the case of early universe torsion as, T ∼ 1 MeV. The gravity part is the Planck mass product with the Holst term. The photon mass in this case yields m2 γ H ∼ 10−69 GeV4. Therefore, in this case, the photon interacts very weakly with spin-torsion matter in Einstein–Cartan (EC) gravity and the strength of the Maxwell–Proca–Holst interaction is much weaker than in the pure gravity sector. For dark photons, this situation changes drastically since a dark photon mass reaches 1.5 GeV, and from this mass and T = 10−3 GeV, one obtains a Maxwell–Proca–Holst strength of 10−6 GeV4, which is now comparable with the gravity sector. Dynamo mechanism competes with the chirality and dissipation by the handness of the magnetic field with respect to the torsion trace vector to regenerate the magnetic field decay. Bombacigno and Mantovani recently found a sign of the Immirzi parameter in the Holst–Nieh–Yan extension of EC gravity. Here, we also find torsion waves for the Immirzi inverse parameter in the sense that this divergence of torsion trace is porportional to the Immirzi field.

Accelerating Earth-bound dark matter

A fraction of the dark matter may consist of a particle species that interacts much more strongly with the Standard Model than a typical weakly interacting massive particle (WIMP) of similar mass. Such a strongly interacting dark matter component could have avoided detection in searches for WIMP-like dark matter through its interactions with the material in the atmosphere and the Earth that slow it down significantly before reaching detectors underground. These same interactions can also enhance the density of a strongly interacting dark matter species near the Earth's surface to well above the local galactic dark matter density. In this work, we propose two new methods of detecting strongly interacting dark matter based on accelerating the enhanced population expected in the Earth through scattering. The first approach is to use underground nuclear accelerator beams to upscatter the ambient dark matter population into a WIMP-style detector located downstream. In the second technique, dark matter is upscattered with an intense thermal source and detected with a low-threshold dark matter detector. We also discuss potential candidates for strongly interacting dark matter, and we show that the scenario can be naturally realized with a hidden fermion coupled to a sub-GeV dark photon.

Belle II sensitivity to long–lived dark photons

In this letter we point out that the BelleII experiment has a unique sensitivity to visibly decaying long-lived dark photons. Concentrating on the signatures with a single high-energy photon in association with a displaced pair of charged particles, we find that BelleII will be able to probe large regions of parameter space that cannot be covered by any other running or proposed experimental facility. While the signature with charged muons or pions in the final state is expected to be background-free after all selections are applied, the case of final state electrons is more involved and requires an in-depth study. We discuss possible ways to further suppress backgrounds and the corresponding experimental prospects.

Searching for inelastic dark matter with future LHC experiments

We consider a dark sector containing a pair of almost degenerate states coupled to the Standard Model through a dark photon mediator. This set-up constitutes a simple realization of the inelastic dark matter scenario. The heaviest dark state is long-lived, in the limit of a small kinetic mixing among the dark photon and the Standard Model hypercharge gauge boson, and/or of a small mass splitting among the dark states. We study the prospects for detection of this scenario at proposed LHC experiments dedicated to search for long-lived particles, namely FASER, MATHUSLA, CODEX-b, AL3X, MAPP, ANUBIS and FACET. We consider both the cases of fermionic and scalar inelastic dark matter. We show that these experimental facilities can probe unexplored regions of the parameter space of this model, and we highlight their complementary roles.

Review of Particle Physics

Abstract The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings. The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app.

Gravitational production of dark photon dark matter with mass generated by the Higgs mechanism

We study the gravitational production of dark photon dark matter during inflation, when dark photons acquire mass by the Higgs mechanism. In the previous study, it was assumed that the dark photon has a Stückelberg mass, or a mass generated by the Higgs mechanism with a sufficiently heavy Higgs boson. In this paper we consider a case in which the Higgs boson is not fully decoupled; the Higgs field changes its vacuum expectation value after inflation. Then, the dark photon mass also changes with time after inflation, and the time evolution of the longitudinal mode is different from the case with a Stückelberg mass. Consequently, the spectrum of the dark photon energy density can have two peaks at an intermediate scale and a small scale. We show that the dark photon can explain the dark matter if its current mass is larger than 6 μeV × (HI /1014 GeV)-4 and smaller than 0.8 GeV × (HI /1014 GeV)-3/2, with HI being the Hubble parameter during inflation. A higher mass is required if one considers a larger gauge coupling constant. The result for the Stückelberg mass can be reproduced in the limit of a small gauge coupling constant. We also comment on the constraints set by various conjectures in quantum gravity theory.

The dark side of the proton

We study the sensitivity of the High-Luminosity LHC to a light baryonic dark photon B, primarily coupled to quarks, as a constituent of the proton. This is achieved by allowing for a dark photon parton distribution function (PDF) in the PDF evolution equations. Depending on the mass and coupling of the dark photon, the evolution of standard quark and gluon PDFs is distorted to varying degrees. By analysing the effect of the dark photon on the tails of Drell-Yan invariant mass distributions, we demonstrate the potential of the LHC in determining competitive bounds on dark photon parameter space.

Dark photon stars: formation and role as dark matter substructure

Any new vector boson with non-zero mass (a 'dark photon' or 'Proca boson') that is present during inflation is automatically produced at this time from vacuum fluctuations and can comprise all or a substantial fraction of the observed dark matter density, as shown by Graham, Mardon, and Rajendran. We demonstrate, utilising both analytic and numerical studies, that such a scenario implies an extremely rich dark matter substructure arising purely from the interplay of gravitational interactions and quantum effects. Due to a remarkable parametric coincidence between the size of the primordial density perturbations and the scale at which quantum pressure is relevant, a substantial fraction of the dark matter inevitably collapses into gravitationally bound solitons, which are fully quantum coherent objects. The central densities of these 'dark photon star', or 'Proca star', solitons are typically a factor 106 larger than the local background dark matter density, and they have characteristic masses of 10-16 M ⊙ (10-5 eV/m)3/2, where m is the mass of the vector.During and post soliton production a comparable fraction of the energy density is initially stored in, and subsequently radiated from, long-lived quasi-normal modes. Furthermore,the solitons are surrounded by characteristic 'fuzzy' dark matter halos in which quantum wave-like properties are also enhanced relative to the usual virialized dark matter expectations.Lower density compact halos, with masses a factor of ∼ 105 greater than the solitons, form at much larger scales. We argue that, at minimum, the solitons are likely to survive to the present day without being tidally disrupted. This rich substructure, which we anticipate also arises from other dark photon dark matter production mechanisms, opens up a wide range of new direct and indirect detection possibilities, as we discuss in a companion paper.

Radiative transfer in stars by feebly interacting bosons

Starting from first principles, we study radiative transfer by new feebly-interacting bosons (FIBs) such as axions, axion-like particles (ALPs), dark photons, and others. Our key simplification is to include only boson emission or absorption (including decay), but not scattering between different modes of the radiation field. Based on a given distribution of temperature and FIB absorption rate in a star, we derive explicit volume-integral expressions for the boson luminosity, reaching from the free-streaming to the strong-trapping limit. The latter is seen explicitly to correspond to quasi-thermal emission from a “FIB sphere” according to the Stefan-Boltzmann law. Our results supersede expressions and approximations found in the recent literature on FIB emission from a supernova core and, for radiatively unstable FIBs, provide explicit expressions for the nonlocal (“ballistic”) transfer of energy recently discussed in horizontal-branch stars.

Molecular Chemistry for Dark Matter. II. Recombination, Molecule Formation, and Halo Mass Function in Atomic Dark Matter

Dissipative dark matter predicts rich observable phenomena that can be tested with future large-scale structure surveys. As a specific example, we study atomic dark matter, consisting of a heavy particle and a light particle charged under a dark electromagnetism. In particular, we calculate the cosmological evolution of atomic dark matter focusing on dark recombination and dark molecule formation. We have obtained the relevant interaction rate coefficients by rescaling the rates for normal hydrogen, and evolved the abundances for ionized, atomic, and molecular states using a modified version of Recfast++ (which we have released publicly at a a https://github.com/jamesgurian/RecfastJulia ). We also provide an analytical approximation for the final abundances. We then calculate the effects of atomic dark matter on the linear power spectrum, which enter through a dark photon diffusion and dark acoustic oscillations. At formation time, the atomic dark matter model suppresses halo abundances on scales smaller than the diffusion scale, just as warm dark matter models suppress the abundance below the free-streaming scale. The subsequent evolution with radiative cooling, however, will alter the halo mass function further.

Commissioning of the PADME experiment with a positron beam

The PADME experiment is designed to search for a hypothetical dark photon A' produced in positron-electron annihilation using a bunched positron beam at the Beam Test Facility of the INFN Laboratori Nazionali di Frascati. The expected sensitivity to the A' -photon mixing parameter ϵ is 10-3, for A' mass ≤ 23.5 MeV/c 2 after collecting ∼ 1013 positrons-on-target. This paper presents the PADME detector status after commissioning in July 2019. In addition, the software algorithms employed to reconstruct physics objects, such as photons and charged particles, and the calibration procedures adopted are illustrated in detail. The results show that the experimental apparatus reaches the design performance, and is able to identify and measure standard electromagnetic processes, such as positron bremsstrahlung and electron-positron annihilation into two photons.

Unitarity constraints and collider searches for dark photons

Dark photons are predicted by various new physics models, and are being intensively studied in a variety of experiments. In the first part of this paper, we obtain partial wave unitarity constraints on the dark photon parameter space from the allowed $VV\rightarrow VV$ scattering processes in the limit of large center-of-mass energy, where $V=W,Z$. In the second part of the paper, searches are performed using the expected differential rates with a realistic detector simulation including a comprehensive set of background processes on dilepton and dilepton plus a photon events at the High Luminosity LHC. In these searches, sensitive differential distributions are used in an optimized way to determine the sensitivity to dark photon parameter space. It is shown that remarkable sensitivity to the dark photon model is achieved and kinetic mixing strength can be probed down to $(1.4-10)\times 10^{-4}$ for dark photon mass between $15$ GeV to $2$ TeV. We also investigate the sensitivity of a future muon collider suggested by the Muon Accelerator Program (MAP) to the dark photon model at different center-of-mass energies. It is shown that a future muon collider is able to reach a sensitivity to kinetic mixing at the order of $10^{-4}$.

Dissecting axion and dark photon with a network of vector sensors

We develop formalisms for a network of vector sensors, sensitive to certain spatial components of the signals, to identify the properties of a light axion or a dark photon background. These bosonic fields contribute to vector-like signals in the detectors, including effective magnetic fields triggering the spin precession, effective electric currents in a shielded room, and forces on the matter. The interplay between a pair of vector sensors and a baseline that separates them can potentially uncover rich information of the bosons, including angular distribution, polarization modes, source localization, and macroscopic circular polarization. Using such a network, one can identify the microscopic nature of a potential signal, such as distinguishing between the axion-fermion coupling and the dipole couplings with the dark photon.

Dark Z at the International Linear Collider

A dark Z is a massive Abelian gauge boson which is coupled to the Standard Model through both kinetic and mass mixing with the electroweak sector. We study the phenomenology of the dark Z at an energy-frontier electron-positron collider, such as the proposed International Linear Collider (ILC). We show that precision electroweak constraints and the current bounds from the hadron colliders allow a dark Z that is kinematically accessible at the ILC with 250 GeV or 500 GeV center-of-mass energy. Further, the reach of the ILC searches for a dark Z significantly exceeds the expected reach of the high luminosity LHC. If a signal consistent with a dark Z is discovered, it would motivate a dedicated run of the ILC at the center-of-mass energy matching the dark Z mass. We demonstrate that a short one month run at design luminosity could measure the dark Z chiral couplings to fermions with percent precision. This measurement can be used to discriminate between competing theoretical models of the resonance: for example, the dark Z can be distinguished from a dark photon with purely kinetic mixing.

Dark Photon Searches via Higgs Boson Production at the LHC and Beyond

Many scenarios beyond the standard model, aiming to solve long-standing cosmological and particle physics problems, suggest that dark matter might experience long-distance interactions mediated by an unbroken dark U(1) gauge symmetry, hence foreseeing the existence of a massless dark photon. Contrary to the massive dark photon, a massless dark photon can only couple to the standard model sector by means of effective higher dimensional operators. Massless dark photon production at colliders will then in general be suppressed at low energy by a UV energy scale, which is of the order of the masses of portal (messenger) fields connecting the dark and the observable sectors. A violation of this expectation is provided by dark photon production mediated by the Higgs boson, thanks to the non-decoupling Higgs properties. Higgs boson production at colliders, followed by the Higgs decay into a photon and a dark photon, provides then a very promising production mechanism for the dark photon discovery, being insensitive in particular regimes to the UV scale of the new physics. This decay channel gives rise to a peculiar signature characterized by a monochromatic photon with energy half the Higgs mass (in the Higgs rest frame) plus missing energy. We show how such resonant photon-plus-missing-energy signature can uniquely be connected to a dark photon production. Higgs boson production and decay into a photon and a dark photon as a source of dark photons is reviewed at the Large Hadron Collider, in light of the present bounds on the corresponding signature by the CMS and ATLAS collaborations. Perspectives for the dark photon production in Higgs-mediated processes at future e+e− colliders are also discussed.

(Invited) Hybridization of Dark Excitons, Bright Excitons, and Photons in an Ultrastrongly Coupled Carbon Nanotube Microcavity and the Importance of Sub-Radiant Polariton States during Relaxation

This talk will present on strong light-matter interaction in optical microcavities incorporating dense semiconducting carbon nanotubes, characterizing hybridization of the bright and dark exciton states of nanotubes, mediated by a cavity photon plus exciton-phonon coupling. This talk will also present on the relaxation of optically excited, bright polariton modes into sub-radiant dark polaritons.