arXiv subjects

Tongyan Lin

Publications and source records attributed to Tongyan Lin.

At least 37 records · Page 2Linked to original sources

arXiv2020

The cosmology of sub-MeV dark matter freeze-in

Dark matter (DM) could be a relic of freeze-in through a light mediator, where the DM is produced by extremely feeble, IR-dominated processes in the thermal Standard Model plasma. In the simplest viable models with the DM mass below the MeV scale, the DM has a small effective electric charge and is born with a nonthermal phase-space distribution. This DM candidate would cause observable departures from standard cosmological evolution. In this work, we combine data from the cosmic microwave background (CMB), Lyman-$α$ forest, quasar lensing, stellar streams, and Milky Way satellite abundances to set a lower limit on freeze-in DM masses up to $\sim 20\,$keV, with the exact constraint depending on whether the DM thermalizes in its own sector. We perform forecasts for the CMB-S4 experiment, the Hydrogen Epoch of Reionization Array, and the Vera Rubin Observatory, finding that freeze-in DM masses up to $\sim 80\,$keV can be explored. These cosmological probes are highly complementary with proposed direct-detection efforts to search for this DM candidate.

astro-ph.CO↗

arXiv2020

SiC Detectors for Sub-GeV Dark Matter

We propose the use of silicon carbide (SiC) for direct detection of sub-GeV dark matter. SiC has properties similar to both silicon and diamond, but has two key advantages: (i) it is a polar semiconductor which allows sensitivity to a broader range of dark matter candidates; and (ii) it exists in many stable polymorphs with varying physical properties, and hence has tunable sensitivity to various dark matter models. We show that SiC is an excellent target to search for electron, nuclear and phonon excitations from scattering of dark matter down to 10 keV in mass, as well as for absorption processes of dark matter down to 10 meV in mass. Combined with its widespread use as an alternative to silicon in other detector technologies and its availability compared to diamond, our results demonstrate that SiC holds much promise as a novel dark matter detector.

hep-ph↗

arXiv2020

Mechanical Quantum Sensing in the Search for Dark Matter

Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.

physics.ins-det↗

arXiv2020

Plasmon production from dark matter scattering

We present a first calculation of the rate for plasmon production in semiconductors from nuclei recoiling against dark matter. The process is analogous to bremsstrahlung of transverse photon modes, but with a longitudinal plasmon mode emitted instead. For dark matter in the 10 MeV - 1 GeV mass range, we find that the plasmon bremsstrahlung rate is 4-5 orders of magnitude smaller than that for elastic scattering, but 4-5 orders of magnitude larger than the transverse bremsstrahlung rate. Because the plasmon can decay into electronic excitations and has characteristic energy given by the plasma frequency $ω_p$, with $ω_p \approx 16$ eV in Si crystals, plasmon production provides a distinctive signature and new method to detect nuclear recoils from sub-GeV dark matter.

hep-ph↗

arXiv2020

Multiphonon excitations from dark matter scattering in crystals

For direct detection of sub-MeV dark matter, a promising strategy is to search for individual phonon excitations in a crystal. We perform an analytic calculation of the rate for light dark matter (keV $<m_{DM}<$ MeV) to produce two acoustic phonons through scattering in cubic crystals such as GaAs, Ge, Si and diamond. The multiphonon rate is always smaller than the rate to produce a single optical phonon, whenever the latter is kinematically accessible. In Si and diamond there is a dark matter mass range for which multiphonon production can be the most promising process, depending on the experimental threshold.

hep-ph↗

arXiv2020

Dynamics of millicharged dark matter in supernova remnants

Dark matter could have a small electromagnetic charge, provided the charge-to-mass ratio is much less than that of electrons or protons. This candidate, commonly known as millicharged dark matter (mDM), would form a plasma and interact with the interstellar medium and electromagnetic fields within galaxies. In general, understanding the dynamics of mDM requires consideration of collective plasma effects. It has been proposed that mDM can be accelerated in supernova remnants, forming a dark cosmic ray population that would leave distinct experimental signatures. In this work, we study a microphysical model where mDM is shocked by a supernova remnant and isotropized in the frame of the expanding fluid. We find that for $|q_χ/m_χ| \gtrsim 10^{-13} e / {\rm MeV}$, the isotropization length for electromagnetic plasma instabilities is much shorter than the size of the supernova remnant. This is a necessary, though not sufficient, first step for formation of a Fermi-accelerated mDM component, and determining the size of this component requires further study. We discuss additional implications of mDM interactions in supernova remnants.

astro-ph.CO↗

arXiv2019

TASI lectures on dark matter models and direct detection

These lectures provide an introduction to models and direct detection of dark matter. We summarize the general features and motivations for candidates in the full dark matter mass range, and then restrict to the keV-TeV mass window. Candidates in this window can be produced by thermal mechanisms in the standard cosmology, and are an important target for experimental searches. We then turn to sub-GeV dark matter (light dark matter) and dark sectors, an area where many new models and experiments are currently being proposed. We discuss the cosmology of dark sectors, specific portal realizations, and some of the prospects for detection. The final parts of these lectures focus on the theory for direct detection, both reviewing the fundamentals for nuclear recoils of WIMPs and describing new directions for sub-GeV candidates. A version of these lectures was originally presented at the TASI 2018 summer school on "Theory in an Era of Data".

hep-ph↗

arXiv2019

Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics

The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later.

astro-ph.CO↗

arXiv2019

Dark Matter Science in the Era of LSST

Astrophysical observations currently provide the only robust, empirical measurements of dark matter. In the coming decade, astrophysical observations will guide other experimental efforts, while simultaneously probing unique regions of dark matter parameter space. This white paper summarizes astrophysical observations that can constrain the fundamental physics of dark matter in the era of LSST. We describe how astrophysical observations will inform our understanding of the fundamental properties of dark matter, such as particle mass, self-interaction strength, non-gravitational interactions with the Standard Model, and compact object abundances. Additionally, we highlight theoretical work and experimental/observational facilities that will complement LSST to strengthen our understanding of the fundamental characteristics of dark matter.

astro-ph.CO↗

arXiv2019

Making dark matter out of light: freeze-in from plasma effects

Dark matter (DM) could couple to particles in the Standard Model (SM) through a light vector mediator. In the limit of small coupling, this portal could be responsible for producing the observed DM abundance through a mechanism known as freeze-in. Furthermore, the requisite DM-SM couplings provide a concrete benchmark for direct and indirect searches for DM. In this paper, we present updated calculations of the relic abundance for DM produced by freeze-in through a light vector mediator. We identify an additional production channel: the decay of photons that acquire an in-medium plasma mass. These plasmon decays are a dominant channel for DM production for sub-MeV DM masses, and including this channel leads to a significant reduction in the predicted signal strength for DM searches. Accounting for production from both plasmon decays and annihilations of SM fermions, the DM acquires a highly non-thermal phase space distribution which impacts the cosmology at later times; these cosmological effects will be explored in a companion paper.

hep-ph↗

arXiv2018

PHOTON-2017 conference proceedings

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $γ\,γ$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $γ$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $γ$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk.

hep-ph↗

arXiv2018

Detection of Light Dark Matter With Optical Phonons in Polar Materials

We show that polar materials are excellent targets for direct detection of sub-GeV dark matter due to the presence of gapped optical phonons as well as acoustic phonons with high sound speed. We take the example of Gallium Arsenide (GaAs), which has the properties needed for experimental realization, and where many results can be estimated analytically. We find GaAs has excellent reach to dark photon absorption, can completely cover the freeze-in benchmark for scattering via an ultralight dark photon, and is competitive with other proposals to detect sub-MeV dark matter scattering off nuclei.

hep-ph↗

arXiv2018

Constraining a Thin Dark Matter Disk with Gaia

If a component of the dark matter has dissipative interactions, it could collapse to form a thin dark disk in our Galaxy that is coplanar with the baryonic disk. It has been suggested that dark disks could explain a variety of observed phenomena, including periodic comet impacts. Using the first data release from the $Gaia$ space observatory, we search for a dark disk via its effect on stellar kinematics in the Milky Way. Our new limits disfavor the presence of a thin dark matter disk, and we present updated measurements on the total matter density in the Solar neighborhood.

astro-ph.GA↗

arXiv2018

Directional Detection of Light Dark Matter with Polar Materials

We consider the direct detection of dark matter (DM) with polar materials, where single production of optical or acoustic phonons gives excellent reach to scattering of sub-MeV DM for both scalar and vector mediators. Using Density Functional Theory (DFT), we calculate the material-specific matrix elements, focusing on GaAs and sapphire, and show that DM scattering in an anisotropic crystal such as sapphire features a strong directional dependence. For example, for a DM candidate with mass 40 keV and relic abundance set by freeze-in, the daily modulation in the interaction rate can be established at 90\% C.L. with a gram-year of exposure. Non-thermal dark photon DM in the meV - eV mass range can also be effectively absorbed in polar materials.

hep-ph↗

arXiv2017

Light Dark Matter: Models and Constraints

We study the direct detection prospects for a representative set of simplified models of sub-GeV dark matter (DM), accounting for existing terrestrial, astrophysical and cosmological constraints. We focus on dark matter lighter than an MeV, where these constraints are most stringent, and find three scenarios with accessible direct detection cross sections: (i) DM interacting via an ultralight kinetically mixed dark photon, (ii) a DM sub-component interacting with nucleons or electrons through a light scalar or vector mediator, and (iii) DM coupled with nucleons via a mediator heavier than ~ 100 keV.

hep-ph↗

arXiv2017

LHC limits on axion-like particles from heavy-ion collisions

In these proceedings we use recent LHC heavy-ion data to set a limit on axion-like particles coupling to electromagnetism with mass in the range 10-100 GeV. We recast ATLAS data as per the strategy proposed in 1607.06083, and find results in-line with the projections given there.

hep-ph↗

arXiv2017

Searching for axion-like particles with ultra-peripheral heavy-ion collisions

We show that ultra-peripheral heavy-ion collisions at the LHC can be used to search for axion-like particles with mass below 100 GeV. The $Z^4$ enhanced photon-photon luminosity from the ions provides a large exclusive production rate, with a signature of a resonant pair of back-to-back photons and no other activity in the detector. In addition, we present both new and updated limits from recasting multi-photon searches at LEP II and the LHC, which are more stringent than those currently in the literature for the mass range 100 MeV to 100 GeV.

hep-ph↗

arXiv2017

Absorption of light dark matter in semiconductors

Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multi-phonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.

hep-ph↗