Light Mediator Research Articles

Neff at CMB challenges U(1)X light gauge boson scenarios

The relativistic degrees of freedom (Neff) is one of the crucial cosmological parameters. The precise measurement of Neff at the time of cosmic microwave background formation, by Planck 2018 can be used to understand the new fundamental interactions, in particular involving light mediators. Presence of any new particle with sufficient energy density and sizeable interactions with Standard Model particles at the temperature around ∼MeV can significantly alter the neutrino decoupling and hence Neff. Thus the bound on Neff can place stringent constraints on various beyond Standard Model paradigms involving light particles. U(1)X models are among such scenarios and are widely studied in several aspects. In this work, we consider several popular U(1)X models with light Z′ boson like U(1)B−L, U(1)B−3Li, U(1)Bi−3Lj, U(1)Li−Lj; i,j=1,2,3 being the flavor indices and study their impact on Neff. We also examine the constraints from ground based experiments like Xenon1T, Borexino, trident, etc. Our analysis shows that for light mass MZ′≲O(MeV) the Neff provides the most stringent constraints on the Z′ mass and coupling, far exceeding the existing constraints from other experiments. Published by the American Physical Society 2024

Constraining light dark matter and mediator with B+→K+νν¯ data

We study the decay of B+ meson into K+ plus a light mediator ϕ, which subsequently decays into a dark matter pair, χ¯χ. Integrating constraints from DM relic density, direct detection, collider data and B-physics, alongside the recently reported results form Belle II experiment, we analyze the couplings between the mediator, standard model fermions, and the dark matter particles. Our results indicate that if the decay process ϕ→χ¯χ is kinematically allowed, i.e., mϕ>2mχ, then the mediator mass must be constrained within 0.35 GeV≲mϕ≲3 GeV. Conversely, if mϕ<2mχ, the mediator mϕ is long-lived relative to the detector size, and the only allowed decay channel is ϕ→e+e−. Published by the American Physical Society 2024

Asymmetric self-interacting dark matter with a canonical seesaw model

We study the possibility of generating dark matter (DM) and baryon asymmetry of the Universe (BAU) simultaneously in an asymmetric DM framework, which also alleviates the small-scale structure issues of cold DM. While the thermal relic of such self-interacting DM remains underabundant due to efficient annihilation into light mediators, a nonzero asymmetry in the dark sector can lead to the survival of the required DM in the Universe. The existence of a light mediator leads to the required self-interactions of DM at small scales while keeping DM properties similar to cold DM at large scales. It also ensures that the symmetric DM component annihilates away, leaving the asymmetric part in the spirit of cogenesis. The particle physics implementation is done in canonical seesaw models of light neutrino mass, connecting it to the origin of DM and BAU. In particular, we consider type-I and type-III seesaw origin of neutrino mass for simplicity and minimality of the field content. We show that the desired self-interactions and relic of DM together with BAU while satisfying relevant constraints lead to strict limits on DM mass O(GeV)≲MDM≲460 GeV. In spite of being a high-scale seesaw, the models remain verifiable in different experiments, including direct and indirect DM searches as well as colliders. Published by the American Physical Society 2024

Enhancement of p-wave dark matter annihilation by quasi-bound states

We scrutinize the Sommerfeld enhancement in dark matter pair annihilation for p-wave and higher-ℓ partial waves. For the Yukawa potential these feature a super-resonant Breit-Wigner peak in their velocity-dependence close to Sommerfeld resonances as well as a universal scaling with velocity for all ℓ ≥ 1 that differs from the s-wave case. We provide a quantum mechanical explanation for these phenomena in terms of quasi-bound states sustained by the centrifugal barrier of the partial-wave potential, and give approximate WKB expressions capturing the main effects. The impact of quasi-bound states is exemplified for wino dark matter and models with light mediators, with a focus on indirect detection signals. We note that quasi-bound states can also explain similar peaks in the bound-state formation and self-scattering cross sections.

Experimental Limits on Solar Reflected Dark Matter with a New Approach on Accelerated-Dark-Matter-Electron Analysis in Semiconductors.

Recently a dark matter-electron (DM-electron) paradigm has drawn much attention. Models beyond the standard halo model describing DM accelerated by high energy celestial bodies are under intense examination as well. In this Letter, a velocity components analysis (VCA) method dedicated to swift analysis of accelerated DM-electron interactions via semiconductor detectors is proposed and the first HPGe detector-based accelerated DM-electron analysis is realized. Utilizing the method, the first germanium based constraint on sub-GeV solar reflected DM-electron interaction is presented with the 205.4 kg·day dataset from the CDEX-10 experiment. In the heavy mediator scenario, our result excels in the mass range of 5-15 keV/c^{2}, achieving a 3 orders of magnitude improvement comparing with previous semiconductor experiments. In the light mediator scenario, the strongest laboratory constraint for DM lighter than 0.1 MeV/c^{2} is presented. The result proves the feasibility and demonstrates the vast potential of the VCA technique in future accelerated DM-electron analyses with semiconductor detectors.

Cosmic-ray boosted dark matter confronted by constraints on new light mediators

Cosmic-ray boosted dark matter confronted by constraints on new light mediators

Extracting halo independent information from dark matter electron scattering data

Direct detection experiments and the interpretation of their results are sensitive to the velocity structure of the dark matter in our galactic halo. In this work, we extend the formalism that deals with such astrophysics-driven uncertainties, originally introduced in the context of dark-matter-nuclear scattering, to include dark-matter-electron scattering interactions. Using mock data, we demonstrate that the ability to determine the correct dark matter mass and velocity distribution is depleted for recoil spectra which only populate a few low-lying bins, such as models involving a light mediator. We also demonstrate how this formalism allows one to test the compatibility of existing experimental data sets (e.g. SENSEI and EDELWEISS), as well as make predictions for possible future experiments (e.g. GaAs-based detectors).

Shedding light on neutrino self-interactions with solar antineutrino searches

Solar antineutrinos are absent in the standard solar model prediction. Consequently, solar antineutrino searches emerge as a powerful tool to probe new physics capable of converting neutrinos into antineutrinos. In this study, we highlight that neutrino self-interactions, recently gaining considerable attention due to their cosmological and astrophysical implications, can lead to significant solar antineutrino production. We systematically explore various types of four-fermion effective operators and light scalar mediators for neutrino self-interactions. By estimating the energy spectra and event rates of solar antineutrinos at prospective neutrino detectors such as JUNO, Hyper-Kamiokande, and THEIA, we reveal that solar antineutrino searches can impose stringent constraints on neutrino self-interactions and probe the parameter space favored by the Hubble tension.

Solar neutrino constraints on light mediators through coherent elastic neutrino-nucleus scattering

Solar neutrino constraints on light mediators through coherent elastic neutrino-nucleus scattering

Disentangle neutrino electromagnetic properties with atomic radiative pair emission

We elaborate the possibility of using the atomic radiative emission of neutrino pair (RENP) to probe the neutrino electromagnetic properties, including magnetic and electric dipole moments, charge radius, and anapole. With the typical 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}(eV) momentum transfer, the atomic RENP is sensitive to not just the tiny neutrino masses but also very light mediators to which the massless photon belongs. The neutrino EM properties introduce extra contribution besides the SM one induced by the heavy W/Z gauge bosons. Since the associated photon spectrum is divided into several sections whose boundaries are determined by the final-state neutrino masses, it is possible to identify the individual neutrino EM form factor elements. Most importantly, scanning the photon spectrum inside the particular section with deviation from the SM prediction once observed allows identification of the neutrino EM form factor type. The RENP provides an ultimate way of disentangling the neutrino EM properties to go beyond the current experimental searches or observations.

Electrochemical C-H/C-C Bond Oxygenation: A Potential Technology for Plastic Depolymerization.

Herein, we provide eco-friendly and safely operated electrocatalytic methods for the selective oxidation directly or with water, air, light, metal catalyst or other mediators serving as the only oxygen supply. Heavy metals, stoichiometric chemical oxidants, or harsh conditions were drawbacks of earlier oxidative cleavage techniques. It has recently come to light that a crucial stage in the deconstruction of plastic waste and the utilization of biomass is the selective activation of inert C(sp3 )-C/H(sp3 ) bonds, which continues to be a significant obstacle in the chemical upcycling of resistant polyolefin waste. An appealing alternative to chemical oxidations using oxygen and catalysts is direct or indirect electrochemical conversion. An essential transition in the chemical and pharmaceutical industries is the electrochemical oxidation of C-H/C-C bonds. In this review, we discuss cutting-edge approaches to chemically recycle commercial plastics and feasible C-C/C-H bonds oxygenation routes for industrial scale-up.

Neff constraints on light mediators coupled to neutrinos: the dilution-resistant effect

We investigate the impact of new light particles, carrying significant energy in the early universe after neutrino decoupling, on the cosmological effective relativistic neutrino species, Neff. If the light particles are produced from decoupled neutrinos, Neff is predominantly modified through the dilution-resistant effect. This effect arises because the energy stored in the mass of new particles is less diluted than the photon and neutrino energy as the universe expands. Our study comprehensively explores this effect, deriving Neff constraints on the couplings of light mediators with neutrinos, encompassing both scalar and vector mediators. We find that the dilution-resistant effect can increase Neff by 0.118 and 0.242 for scalar and vector mediators, respectively. These values can be readily reached by forthcoming CMB experiments. Upon reaching these levels, future Neff constraints on the couplings will be improved by many orders of magnitude.

Direct detection of cosmic ray-boosted puffy dark matter

For the light relativistic dark matter (DM) boosted by high energy cosmic ray, its scattering cross section with the nucleon is sensitively dependent on the momentum-transfer and such an dependence is caused by the mediator in the scattering. For puffy DM particle with a size, the momentum-transfer dependence can also arise from the DM radius effect. All these momentum-transfer dependences should be considered. In this note we study the direct detection limits on the cosmic ray-boosted puffy DM for a simplified model with a light mediator. For comparison, we first re-derive the direct detection limits on the cosmic ray-boosted point-like DM. We display the limits on various planes of parameters and find that the limits for the cosmic ray-boosted puffy DM are stronger than for the point-like DM.

Decay of the mediator particle at threshold

A light mediator particle is often predicted in the dark sector scenario, which weakly interacts with the standard model (SM) particles. The weakness of the interaction is usually described by a small coupling; however, the small coupling does not always guarantee the weakness of the interaction. When the mass of the mediator particle lies in a threshold region, the so-called threshold singularity may emerge, and then the perturbative calculation fails. This singularity causes several effects, e.g., the mixing between the mediator particle and bound states, the Sommerfeld effect on the final state of the mediator particle decay, etc. Taking the minimal model of the vector mediator particle decaying mainly into the SM particles as an example, we develop a method to describe the singularity quantitatively. We also calculate some physical quantities using this method, such as the lifetime of the mediator particle and find that those could be significantly altered compared with the result of the perturbative calculation.

Can Neutrino Self-interactions Save Sterile Neutrino Dark Matter?

Sterile neutrinos only interact with the standard model through the neutrino sector, and thus represent a simple dark matter (DM) candidate with many potential astrophysical and cosmological signatures. Recently, sterile neutrinos produced through self-interactions of active neutrinos have received attention as a particle candidate that can yield the entire observed DM relic abundance without violating the most stringent constraints from X-ray observations. We examine consistency of this production mechanism with the abundance of small-scale structure in the universe, as captured by the population of ultrafaint dwarf galaxies orbiting the Milky Way, and derive a lower bound on the sterile-neutrino particle mass of 37 keV. Combining these results with previous collider and X-ray limits excludes 100% sterile-neutrino DM produced by strong neutrino self-coupling, mediated by a heavy (≳1 GeV) scalar; however, data permits sterile-neutrino DM production via a light mediator.

Probing dark QCD sector through the Higgs portal with machine learning at the LHC

The QCD-like dark sector with GeV-scale dark hadrons has the potential to generate new signatures at the Large Hadron Collider (LHC). In this paper, we consider a singlet scalar mediator in the tens of GeV-scale that connects the dark sector and the Standard Model (SM) sector via the Higgs portal. We focus on the Higgs-strahlung process, qoverline{q} ′ → W* → WH, to produce a highly boosted Higgs boson. Our scenario predicts two different processes that can generate dark mesons: (1) the cascade decay from the Higgs boson to two light scalar mediators and then to four dark mesons; (2) the Higgs boson decaying to two dark quarks, which then undergo a QCD-like shower and hadronization to produce dark mesons. We apply machine learning techniques, such as Convolutional Neural Network (CNN) and Energy Flow Network (EFN), to the fat-jet structure to distinguish these signal processes from large SM backgrounds. We find that the branching ratio of the Higgs boson to two light scalar mediators can be constrained to be less than about 10% at 14 TeV LHC with mathcal{L} = 3000 fb−1.

Probing generalized neutrino interactions with the DUNE Near Detector

We explore the prospects of constraining general non standard interactions involving light mediators through elastic neutrino-electron scattering events at the DUNE Near Detector (ND). We furthermore consider the special cases of light vector mediators in motivated models such as U(1)B−L, textrm{U}{(1)}_{L_{mu }-{L}_{tau }} , E6 and left-right symmetry. The present analysis is based on detailed Monte Carlo simulations of the expected DUNE-ND signal taking into account detector resolution effects, realistic backgrounds as well as On-Axis and Off-Axis neutrino spectra. We show that the high intensity neutrino beam available at Fermilab can place competitive constraints surpassing those of low-energy neutrino searches and direct detection dark matter experiments.

Search for Light Dark Matter from the Atmosphere in PandaX-4T.

We report a search for light dark matter produced through the cascading decay of η mesons, which are created as a result of inelastic collisions between cosmic rays and Earth's atmosphere. We introduce a new and general framework, publicly accessible, designed to address boosted dark matter specifically, with which a full and dedicated simulation including both elastic and quasielastic processes of Earth attenuation effect on the dark matter particles arriving at the detector is performed. In the PandaX-4T commissioning data of 0.63 tonne·year exposure, no significant excess over background is observed. The first constraints on the interaction between light dark matter generated in the atmosphere and nucleus through a light scalar mediator are obtained. The lowest excluded cross section is set at 5.9×10^{-37} cm^{2} for a dark matter mass of 0.1 MeV/c^{2} and mediator mass of 300 MeV/c^{2}. The lowest upper limit of η to the dark matter decay branching ratio is 1.6×10^{-7}.

Attenuation of cosmic-ray up-scattered dark matter

GeV-scale dark matter particles with strong coupling to baryons evade the standard direct detection limits as they are efficiently stopped in the overburden and, consequently, are not able to reach the underground detectors. On the other hand, it has been shown that it is possible to probe this parameter space taking into account the flux of dark matter particles boosted by interactions with cosmic rays. We revisit these bounds paying particular attention to interactions of the relativistic dark matter particles in the Earth’s crust. The effects of nuclear form factors, inelastic scattering and extra dependence of the cross section on transferred momentum (e.g. due to presence of light mediators) are studied and are found to be crucial for answering the question as to whether the window for GeV-scale strongly interacting dark matter is closed or not.

Light thermal relics enabled by a second Higgs

Sub-GeV thermal relic dark matter typically requires the existence of a light mediator particle. We introduce the light two-Higgs-doublet portal, illustrated by a minimal UV-complete model for sub-GeV dark matter with kinematically forbidden annihilations into leptons. All new physics states in this scenario lie at or below the electroweak scale, affecting Higgs physics, the muon anomalous magnetic moment and potentially neutrino masses. Observation of radiative dark matter annihilation by future MeV gamma-ray telescopes would be key to unambiguously identify the scenario.