Conventional lore from Tremaine and Gunn excludes fermionic dark matter lighter than a few hundred eV, based on the Pauli exclusion principle. We highlight a simple way of evading this bound with a large number of species that leads to numerous non-trivial consequences. In this scenario there are many distinct species of fermions with quasi-degenerate masses and no couplings to the standard model. Nonetheless, gravitational interactions lead to constraints from measurements at the LHC, of cosmic rays, of supernovae, and of black hole spins and lifetimes. We find that the LHC constrains the number of distinct species, bosons or fermions lighter than $\sim 500$ GeV, to be $N \lesssim 10^{62}$. This, in particular, implies that roughly degenerate fermionic dark matter must be heavier than $\sim 10^{-14}$ eV, which thus relaxes the Tremaine-Gunn bound by $\sim 16$ orders of magnitude. Slightly weaker constraints applying to masses up to $\sim100$ TeV exist from cosmic ray measurements while various constraints on masses $\lesssim10^{-10}$ eV apply from black hole observations. We consider a variety of phenomenological bounds on the number of species of particles. Finally, we note that there exist theoretical considerations regarding quantum gravity which could impose more severe constraints that may limit the number of physical states to $N\lesssim 10^{32}$.
The coherent oscillation of ultralight dark matter in the mass regime around $10^{-23}$ eV induces changes in gravitational potential with the frequency in the nanohertz range. This effect is known to produce a monochromatic signal in the pulsar timing residuals. Here we discuss a multifield scenario that produces a wide spectrum of frequencies, such that the ultralight particle oscillation can mimic the pulsar timing signal of stochastic common spectrum process. We discuss how ultralight dark matter with various spins produces such a wide band spectrum on pulsar timing residuals and perform t…
Angular correlation and deformed Hellings-Downs curve from spin-2 ultralight dark matter
School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS（基础物理与数学科学学院，杭州高等研究院，中国科学院大学）；School of Physical Science and Technology, Ningbo University（宁波大学物理科学与技术学院）；CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所，理论物理国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）；National Astronomy Observatories, Chinese Academy of Science（中国科学院国家天文台）；International Center for Theoretical Physics Asia-Pacific（亚太理论物理中心）
Ultralight dark matter is a compelling dark matter candidate. In this work, we examine the impact of quadratically-coupled ultralight dark matter on the predictions of Big Bang Nucleosynthesis. The presence of ultralight dark matter can modify the effective values of fundamental constants during Big Bang Nucleosynthesis, modifying the predicted abundances of the primordial elements such as Helium-4. We improve upon the existing literature in two ways: firstly, we take into account the thermal mass acquired by the ultralight dark matter due to its quadratic interactions with the Standard Model …
Cosmological mechanisms that yield ultralight dark matter are insensitive to the intrinsic parity of a bosonic dark matter candidate, but that same quantity plays a crucial role in a direct detection experiment. The modification of electrodynamics in the presence of ultralight axion-like dark matter is well-known and has been used to realize sensitive probes of such sub-eV mass-scale dark matter, and analogous studies exist for hidden-photon dark matter as well. Here we reframe the modification of electrodynamics for ultralight dark matter of positive intrinsic parity, with a focus on the scal…
Warm dark matter has recently become increasingly constrained by observational inferences about the low-mass end of the subhalo mass function, which would be suppressed by dark matter free streaming in the early Universe. In this work, we point out that a constraint can be placed on ultralight bosonic dark matter (often referred to as "fuzzy dark matter") based on similar considerations. Recent limits on warm dark matter from strong gravitational lensing of quasars and from fluctuations in stellar streams separately translate to a lower limit of $\sim 2.1 \times 10^{-21}$ eV on the mass of an …
We explore the neutrinoless double beta ($0νββ$) decay induced by an ultralight dark matter field coupled to neutrinos. The effect on $0νββ$ decay is significant if the coupling violates the lepton number, for which the $ΔL=2$ transition is directly driven by the dark matter field without further suppression of small neutrino masses. As the ultralight dark matter can be well described by a classical field, the effect features a periodic modulation pattern in decay events. However, we find that in the early Universe such coupling will be very likely to alter the standard cosmological results. I…
If ultralight $(\ll$ eV), bosonic dark matter couples to right handed neutrinos, active neutrino masses and mixing angles depend on the ambient dark matter density. When the neutrino Majorana mass, induced by the dark matter background, is small compared to the Dirac mass, neutrinos are "pseudo-Dirac" fermions that undergo oscillations between nearly degenerate active and sterile states. We present a complete cosmological history for such a scenario and find severe limits from a variety of terrestrial and cosmological observables. For scalar masses in the "fuzzy" dark matter regime ($\sim 10^{…
We investigate the influence of a dark photon on the Casimir effect and calculate the corresponding leading contribution to the Casimir energy. For expected magnitudes of the photon - dark photon mixing parameter, the influence turns out to be negligible. The plasmon dispersion relation is also not noticeably modified by the presence of a dark photon.
Background-Induced Forces from Quadratically Coupled Ultralight Dark Matter
Cincinnati State Technical and Community College（辛辛那提州立技术与社区学院）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器中心 DESY）；Shanghai Jiao Tong University（上海交通大学）；University of Oregon（俄勒冈大学）
We study how neutrino oscillations could probe the existence of ultralight bosonic dark matter. Three distinct signatures on neutrino oscillations are identified, depending on the mass of the dark matter and the specific experimental setup. These are time modulation signals, oscillation probability distortions due to fast modulations, and fast varying matter effects. We provide all the necessary information to perform a bottom-up, model-independent experimental analysis to probe such scenarios. Using the future DUNE experiment as an example, we estimate its sensitivity to ultralight scalar dar…
Precision Solar System Dynamics for Ultralight Dark Matter Search
Sapienza Università di Roma（罗马大学）；INFN Roma1（意大利国家核物理研究所罗马第一分部）；Université Paris-Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；CEA（法国原子能和替代能源委员会）；Institut de Physique Théorique（理论物理研究所）；Universität Bonn（波恩大学）
Galactic magnetic fields seeded by ultralight dark photons
Colorado State University（科罗拉多州立大学）；University of Pittsburgh（匹兹堡大学）；Queen’s University（女王大学）；Arthur B. McDonald Canadian Astroparticle Physics Research Institute（阿瑟·B·麦克唐纳加拿大天体粒子物理研究所）；Perimeter Institute for Theoretical Physics（理论物理前沿研究所）；York University（约克大学）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）
We reconsider entropy arguments which have been previously argued to support the idea that the dark matter constituents are primordial black holes with many solar masses. It has recently been shown that QCD axions which solve the strong CP problem may have masses $m_a$ in the extended range $10^{-3}eV > m_a > 10^{-33} eV$. Ultralight axions provide so many degrees of freedom that their entropy can exceed that of primordial black holes. This suggests that ultralight axions are more suited than primordial black holes to be constituents of dark matter.
We look for and place observational constraints on the imprint of ultralight dark matter (ULDM) soliton cores in rotation-dominated galaxies. Extending previous analyses, we find a conservative constraint which disfavors the soliton-host halo relation found in some numerical simulations over a broad range in the ULDM particle mass $m$. Combining the observational constraints with theoretical arguments for the efficiency of soliton formation via gravitational dynamical relaxation, and assuming that the soliton-halo relation is correct, our results disfavor ULDM from comprising 100\% of the tota…
If dark matter is ultralight, the number density of dark matter is very high and the techniques of zero-temperature field theory are no longer valid. The dark matter number density modifies the vacuum giving it a non-negligible particle occupation number. For fermionic dark matter, this occupation number can be no larger than one. However, in the case of bosons the occupation number is unbounded. If there is a large occupation number, the Bose enhancement needs to be taken into consideration for any process involving particles which interact with the dark matter. Because the occupation number …
SpaceQ -- Direct Detection of Ultralight Dark Matter with Space Quantum Sensors
University of California, Irvine（加州大学尔湾分校）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；University of Chicago（芝加哥大学）；The University of Tokyo（东京大学）；University of Delaware（特拉华大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；University of Maryland（马里兰大学）
Gravitational-wave (GW) detectors that monitor fluctuations in the separation between inertial test masses (TMs) are sensitive to new forces acting on those TMs. Ultralight dark-photon dark matter (DPDM) coupled to $U(1)_B$ or $U(1)_{B-L}$ charges supplies one such force that oscillates with a frequency set by the DPDM mass. GW detectors operating in different frequency bands are thus sensitive to different DPDM mass ranges. A recent GW detection proposal based on monitoring the separation of certain asteroids in the inner Solar System would have sensitivity to $μ$Hz frequencies [arXiv:2112.11…
