Dark Photon Research Articles

Neutrinos, dark matter and Higgs vacua in parity solutions of the strong CP problem

The strong CP problem can be solved if the laws of nature are invariant under a space-time parity exchanging the Standard Model with its mirror copy. We review and extend different realizations of this idea with the aim of discussing Dark Matter, neutrino physics, leptogenesis and collider physics within the same context. In the minimal realization of ref. [1] the mirror world contains a massless dark photon, which leads to a rather interesting cosmology. Mirror electrons reproduce the dark matter abundance for masses between 500–1000 GeV with traces of strongly interacting dark matter. This scenario also predicts deviations from cold dark matter, sizable ∆Neff and colored states in the TeV range that will be tested in a variety of upcoming experiments. We also explore scenarios where the mirror photon is massive and the mirror particles are charged under ordinary electromagnetism with very different phenomenology. We also show that, for the measured values of the SM parameters, the Higgs effective potential can give rise to a second minimum at large field value as required to break spontaneously the parity symmetry.

Dark photons from charged pion bremsstrahlung at proton beam experiments

Dark photons from charged pion bremsstrahlung at proton beam experiments

Riding the dark matter wave: Novel limits on general dark photons from LISA Pathfinder

We note the possibility to perform a parametrically improved search for gauged baryon (B) and baryon minus lepton (B−L) Dark Photon Dark Matter (DPDM) using auxiliary channel data from LISA Pathfinder. In particular we use the measurement of the differential movement between the test masses (TMs) and the space craft (SC) which is nearly as sensitive as the tracking between the two TMs. TMs and SC are made from different materials and therefore have different charge-to-mass ratios for both B−L and B. Thus, the surrounding DPDM field induces a relative acceleration of nearly constant frequency. For the case of B−L, we find that LISA Pathfinder can constrain previously unexplored parameter space, providing the world leading limits in the mass range 4⋅10−19eV<m<3⋅10−17eV. This limit can easily be recast also for dark photons that arise from gauging other global symmetries of the SM.

Search for Boosted Dark Matter in COSINE-100.

We search for energetic electron recoil signals induced by boosted dark matter (BDM) from the galactic center using the COSINE-100 array of NaI(Tl) crystal detectors at the Yangyang Underground Laboratory. The signal would be an excess of events with energies above 4MeV over the well-understood background. Because no excess of events are observed in a 97.7 kg·yr exposure, we set limits on BDM interactions under a variety of hypotheses. Notably, we explored the dark photon parameter space, leading to competitive limits compared to direct dark photon search experiments, particularly for dark photon masses below 4MeV and considering the invisible decay mode. Furthermore, by comparing our results with a previous BDM search conducted by the Super-Kamionkande experiment, we found that the COSINE-100 detector has advantages in searching for low-mass dark matter. This analysis demonstrates the potential of the COSINE-100 detector to search for MeV electron recoil signals produced by the dark sector particle interactions.

New constraint on dark photon at T2K off-axis near detector

The T2K experiment is one of the most powerful long-baseline experiments to investigate neutrino oscillations. The off-axis near detector called ND280 is installed 280 m downstream from the neutrino production target to measure the neutrino energy spectrum. In this paper, we study the capability of the ND280 detector to search for the dark photon produced through the meson rare decay and proton bremsstrahlung processes at the proton beam dump. We find that the ten-year operation of T2K with the ND280 detector excludes the unexplored parameter region for the dark photon mass and kinetic mixing. We also show that a broader parameter region can be searched by the ND280 in the future T2K operation for dark photon as well as U(1)B−L gauge boson.

Cosmologically varying kinetic mixing

The portal connecting the invisible and visible sectors is one of the most natural explanations of the dark world. However, the early-time dark matter production via the portal faces extremely stringent late-time constraints. To solve such tension, we construct the scalar-controlled kinetic mixing varying with the ultralight CP-even scalar’s cosmological evolution. To realize this and eliminate the constant mixing, we couple the ultralight scalar within 10−33eV ≲ m0 ≪ eV with the heavy doubly charged messengers and impose the ℤ2 symmetry under the dark charge conjugation. Via the varying mixing, the keV – MeV dark photon dark matter is produced through the early-time freeze-in when the scalar is misaligned from the origin and free from the late-time exclusions when the scalar does the damped oscillation and dynamically sets the kinetic mixing. We also find that the scalar-photon coupling emerges from the underlying physics, which changes the cosmological history and provides the experimental targets based on the fine-structure constant variation and the equivalence principle violation. To ensure the scalar naturalness, we discretely re-establish the broken shift symmetry by embedding the minimal model into the ℤN-protected model. When N ~ 10, the scalar’s mass quantum correction can be suppressed much below 10−33eV.

Spin-1 thermal targets for dark matter searches at beam dump and fixed target experiments

The current framework for dark matter (DM) searches at beam dump and fixed target experiments primarily relies on four benchmark models, the so-called complex scalar, inelastic scalar, pseudo-Dirac and finally, Majorana DM models. While this approach has so far been successful in the interpretation of the available data, it a priori excludes the possibility that DM is made of spin-1 particles — a restriction which is neither theoretically nor experimentally justified. In this work we extend the current landscape of sub-GeV DM models to a set of models for spin-1 DM, including a family of simplified models (involving one DM candidate and one mediator — the dark photon) and an ultraviolet complete model based on a non-abelian gauge group where DM is a spin-1 Strongly Interacting Massive Particle (SIMP). For each of these models, we calculate the DM relic density, the expected number of signal events at beam dump experiments such as LSND and MiniBooNE, the rate of energy injection in the early universe thermal bath and in the Intergalactic Medium (IGM), as well as the helicity amplitudes for forward processes subject to the unitary bound. We then compare these predictions with experimental results from Planck, CMB surveys, IGM temperature observations, LSND, MiniBooNE, NA64, and BaBar and with available projections from LDMX and Belle II. Through this comparison, we identify the regions in the parameter space of the models considered in this work where DM is simultaneously thermally produced, compatible with present observations, and within reach at Belle II and, in particular, at LDMX. We find that the simplified models considered here are strongly constrained by current beam dump experiments and the unitarity bound, and will thus be conclusively probed (i.e. discovered or ruled out) in the first stages of LDMX data taking. We also find that the vector SIMP model explored in this work predicts the observed DM relic abundance, is compatible with current observations and within reach at LDMX in a wide region of the parameter space of the theory.

Latest Results on the Search of Dark Photons with a Multicathode Counter

The method of measurements is described that has been performed using a multicathode counter with an iron cathode. The aim of experiment was to search for diurnal variations of the countrate of single electrons emitted from the surface of the cathode by the conversion of dark photons on its surface. The results obtained during 160 days of measurements are presented.

The future search for low-frequency axions and new physics with the FLASH resonant cavity experiment at Frascati National Laboratories

We present a proposal for a new experiment, the FINUDA magnet for Light Axion SearcH (FLASH), a large resonant-cavity haloscope in a high static magnetic field which is planned to probe new physics in the form of dark matter (DM) axions, scalar fields, chameleons, hidden photons, as well as high frequency gravitational waves (GWs). Concerning the QCD axion, FLASH will search for these particles as the DM in the mass range (0.49–1.49)μeV, thus filling the mass gap between the ranges covered by other planned searches. A dedicated Microstrip SQUID operating at ultra-cryogenic temperatures will amplify the signal. The frequency range accessible overlaps with the Very High Frequency (VHF) range of the radio wave spectrum and allows for a search in GWs in the frequency range (100–300)MHz. The experiment will make use of the cryogenic plant and magnet of the FINUDA experiment at INFN Frascati National Laboratories near Rome (Italy); the operations needed to restore the functionalities of the apparatus are currently underway. We present the setup of the experiment and the sensitivity forecasts for the detection of axions, scalar fields, chameleons, hidden photons, and GWs.

A Proposal for a Low‐Frequency Axion Search in the 1–2 μ$\umu$ eV Range and Below with the BabyIAXO Magnet

AbstractIn the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom‐made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m3. In this document, it proposes and describe the implementation of low‐frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion‐photon coupling down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2 eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5‐meter‐long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed will also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range ( eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as an appropriate low‐noise signal amplification and detection chain.

Contributions of inert electroweak multiplets to Higgs properties

New physics could manifest itself in the form of electroweak multiplets that interact at tree level with the Higgs boson but do not mix with Standard Model fields or acquire expectation values. In this paper, we study the potential contributions of such inert multiplets to several crucial Higgs properties, namely, the branching ratio of the Higgs to a Z boson and a photon (or massless dark photon) and the triple Higgs coupling. Constraints from the Higgs signal strengths, oblique parameters and unitarity are taken into account.

Dark matter from the centre of SU(N)

A dark sector with non-abelian gauge symmetry provides a sound framework to justify stable dark matter (DM) candidates. We consider scalar fields charged under a SU(N)SU(N) gauge group, and show that the centre of SU(N)SU(N), the discrete subgroup Z_NZN also known as NN-ality, can ensure the stability of scalar DM particles. We analyse in some details two minimal DM models of this class, based on SU(2)SU(2) and SU(3)SU(3), respectively. These models have non-trivial patterns of spontaneous symmetry breaking, leading to distinctive phenomenological implications. For the SU(2)SU(2) model these include a specific interplay of two DM states, with the same interactions but different masses, and several complementary DM annihilation regimes, either within the dark sector or through the Higgs portal. The SU(3)SU(3) model predicts dark radiation made of a pair of dark photons with a unique gauge coupling, as well as regimes where DM semi-annihilations become dominant and testable.

Single Parameter Matching of Ordinary and Novel (Dark Matter) Particles From Their Physical Equalities to Their Physical Differences

Novel (dark matter) particles, while known to exist, refuse to show up explicitly. Theoretical approaches within the Standard&#x0D; Model (SM) as for example, looking for the dark photon with Feynman diagrams, in the process &amp;gamma;&amp;gamma; &amp;minus;&amp;rarr; e+e , is&#x0D; still inconclusive (Xu, I. et al., 2022). However, empirical-like methods can give the proof about the existence of dark&#x0D; matter, see for instance (Clowe, D. et al., 2006). Hence it is reasonable trying to understand as to why ordinary and novel&#x0D; (dm) particles differ so much from each other. This we wish to do with solutions of the bicubic equation for particle&#x0D; limiting velocities ( ˇ Soln, J., 2014-2022). Once we have the solutions for novel and ordinary particle limiting velocities&#x0D; from ( ˇ Soln, J. 2021.1.2, 2022), we first establish, with the help of evolutionary congruent parameters, ordinary z1 and&#x0D; novel z2, satisfying z1 ⪯ 1and z2 ⪰ 1,the smooth matching point of equal values for ordinary and novel particles at&#x0D; z1 = z2 = 1. At this point the limiting velocities and other physical quantities of ordinary and novel particles have&#x0D; equal values, which can be also characterized by z1&amp;times; z2 = 1; this, consistent with Discriminants of ordinary and novel&#x0D; limiting velocity solutions, is extended everywhere, so that z2 = 1/ z1. the novel particle limiting velocity solutions&#x0D; reveal congruent angle &amp;alpha;, contained now in z1 and z2, and as such can also serve as another evolutionary parameter. The&#x0D; smooth matching point is now &amp;alpha; = &amp;pi;/2. If physically equivalent ordinary and novel particles move away from this point&#x0D; to &amp;alpha; ̸= &amp;pi;/2, they will physically be different from each other. In other words, the novel particle is in z2 ⪰ 1 territory, and&#x0D; the ordinary particle is in z1 ⪯ 1 territory and direct interactions are likely impossible. With this formalism, we investigate&#x0D; physical differences between ordinary and novel particles, when moving away from &amp;alpha; = &amp;pi;/2. In tis article, we largely&#x0D; are dealing with high energy leptons together with relevant photons with congruent parameter ranges of 0 ≺ &amp;alpha; ⪯ &amp;pi;/2,&#x0D; 0 ≺ z1 ⪯ 1,&amp;infin;≻ z2 ⪰ 1. In fact due to a large interest in photons, here, within this formalism, we evaluate very precisely&#x0D; limiting velocities for the ordinary and novel photons. From these evaluations, we deduce numerically that congruent angles&#x0D; of novel and ordinary photons are related through the quantum jump &amp;alpha;(&amp;gamma;N) = 2&amp;alpha;(&amp;gamma;), which is verified also for other&#x0D; particles. Hence, the general quantum jump between congruent angles of limiting velocities associated with ordinary and&#x0D; novel particles is &amp;alpha;(xN) = &amp;alpha;(x), where x = &amp;gamma;, e, &amp;nu;, etc. The congruent angle quantum jump connects every ordinary&#x0D; particle, such as electron e, or neutrino &amp;nu;,respectively, to novel electron eN and novel neutrino &amp;nu;N. This, definitively is a&#x0D; rather simple way to identify novel particles. All that one needs is to find them.

Search for Light Dark Matter with NA64 at CERN.

Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A^{'}, in collisions of 100GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×10^{11} electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A^{'} couplings to photons for masses m_{A^{'}}≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A^{'} coupling α_{D}≤0.1 for masses 0.001≲m_{χ}≲0.1 GeV and 3m_{χ}≤m_{A^{'}}.

New physics in multi-electron muon decays

We study the exotic muon decays with five charged tracks in the final state. First, we investigate the Standard Model rate for μ+ → 3e+ 2e− 2ν (B\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B} $$\\end{document} = 4.0 × 10−10) and find that the Mu3e experiment should have tens to hundreds of signal events per 1015μ+ decays, depending on the signal selection strategy. We then turn to a neutrinoless μ+ → 3e+ 2e− decay that may arise in new-physics models with lepton-flavor-violating effective operators involving a dark Higgs hd. Following its production in μ+ → e+hd decays, the dark Higgs can undergo a decay cascade to two e+e− pairs through two dark photons, hd→ γdγd→ 2(e+e−). We show that a μ+→ 3e+ 2e− search at the Mu3e experiment, with potential sensitivity to the branching ratio at the O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(10−12) level or below, can explore new regions of parameter space and new physics scales as high as Λ ∼ 1015 GeV.

Nanohertz gravitational waves from cosmic strings and dark photon dark matter

The recent observations by pulsar timing array (PTA) experiments suggest the existence of stochastic gravitational wave background in the nano-Hz range. It can be a hint for the new physics and cosmic string is one of the promising candidates. In this paper, we study the implication of the PTA result for cosmic strings and dark photon dark matter produced by the decay of cosmic string loops. It can simultaneously explain the PTA result and present dark matter abundance for the dark photon mass m∼10−7–10−5eV. Implications for the gravitational wave detection with multi-frequency bands are also discussed.

Global QCD analysis and dark photons

We perform a global QCD analysis of high energy scattering data within the JAM Monte Carlo framework, including a coupling to a dark photon that augments the Standard Model (SM) electroweak coupling via kinetic mixing with the hypercharge B boson. We first set limits on the dark photon mass and mixing parameter assuming that the SM is the true theory of Nature, taking into account also the effect on g – 2 of the muon. If instead we entertain the possibility that the dark photon may play a role in deep-inelastic scattering (DIS), we find that the best fit is preferred over the SM at 6.5σ, even after accounting for missing higher order uncertainties. The improvement in χ2 with the dark photon is stable against all the tests we have applied, with the improvements in the theoretical predictions spread across a wide range of x and Q2. The largest improvement corresponds to the fixed target and HERA DIS data, while the best fit yields a value of g – 2 which significantly reduces the disagreement with the latest experimental determination.

Search for dark photon decays to μ+μ− at NA62

The NA62 experiment at CERN, designed to study the ultra-rare decay K+ → π+νν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \\overline{\ u} $$\\end{document}, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ+μ− pairs is reported, based on a sample of 1.4 × 1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV/c2.

Reflections on bubble walls

We discuss the dynamics of expanding bubble walls in the presence of massive dark photons whose mass changes as they cross the wall. For sufficiently thin walls, we show that there exists a transient kinematic regime characterized by a constant reflection probability of longitudinal — but not transverse — modes. This effect can have important implications for the dynamics of expanding vacuum bubbles in the early Universe. Most notably, it leads to a new source of pressure on the expanding interface, featuring a non-monotonic dependence on the γ-factor of the bubble walls and reaching a peak at intermediate γ-factors that we dub Maximum Dynamic Pressure. When this pressure is large enough to halt the acceleration of the bubble walls, the difference in vacuum energy densities goes into making a fraction of the dark photons relativistic, turning them into dark radiation. If the dark radiation remains relativistic until late times, an observable contribution to ∆Neff is possible for phase transitions with strength α ∼ 10−2− 10−1.

Production rates of dark photons and Z' in the Sun and stellar cooling bounds

Light weakly interacting particles could be copiouslyproduced in the Sun which, as a well-understood star, could providesevere constraints on such new physics. In this work, we calculatethe solar production rates of light gauge bosons (e.g. dark photon)arising from various U(1) extensions of the standard model. Itis known that the dark photon production rate is suppressed by thedark photon mass if it is well below the plasmon mass of the medium.We show that for more general U(1) gauge bosons, this suppressionis absent if the couplings are not in alignment with those of thephoton. We investigate a few frequently discussed U(1) models including B - L, Lμ - Lτ , and Le - Lμ(τ) , and derivethe stellar cooling bounds for these models.