3,757 research outputs found
Superradiance in rotating stars and pulsar-timing constraints on dark photons
In the presence of massive bosonic degrees of freedom, rotational
superradiance can trigger an instability that spins down black holes. This
leads to peculiar gravitational-wave signatures and distribution in the
spin-mass plane, which in turn can impose stringent constraints on ultralight
fields. Here, we demonstrate that there is an analogous spindown effect for
conducting stars. We show that rotating stars amplify low frequency
electromagnetic waves, and that this effect is largest when the time scale for
conduction within the star is of the order of a light crossing time. This has
interesting consequences for dark photons, as massive dark photons would cause
stars to spin down due to superradiant instabilities. The time scale of the
spindown depends on the mass of the dark photon, and on the rotation rate,
compactness, and conductivity of the star. Existing measurements of the
spindown rate of pulsars place direct constraints on models of dark sectors.
Our analysis suggests that dark photons of mass eV are
excluded by pulsar-timing observations. These constraints also exclude
superradiant instabilities triggered by dark photons as an explanation for the
spin limit of observed pulsars.Comment: 13 pages, 4 figure
Collider Searches for Long-Lived Particles Beyond the Standard Model
Experimental tests of the Standard Model of particle physics (SM) find
excellent agreement with its predictions. Since the original formation of the
SM, experiments have provided little guidance regarding the explanations of
phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor
have we understood the aesthetic and theoretical problems of the SM, despite
years of searching for physics beyond the Standard Model (BSM) at particle
colliders. Some BSM particles can be produced at colliders yet evade being
discovered, if the reconstruction and analysis procedures not matched to
characteristics of the particle. An example is particles with large lifetimes.
As interest in searches for such long-lived particles (LLPs) grows rapidly, a
review of the topic is presented in this article. The broad range of
theoretical motivations for LLPs and the experimental strategies and methods
employed to search for them are described. Results from decades of LLP searches
are reviewed, as are opportunities for the next generation of searches at both
existing and future experiments.Comment: 79 pages, 36 figures, submitted to Progress in Particle and Nuclear
Physic
Searching for Dark Absorption with Direct Detection Experiments
We consider the absorption by bound electrons of dark matter in the form of
dark photons and axion-like particles, as well as of dark photons from the Sun,
in current and next-generation direct detection experiments. Experiments
sensitive to electron recoils can detect such particles with masses between a
few eV to more than 10 keV. For dark photon dark matter, we update a previous
bound based on XENON10 data and derive new bounds based on data from XENON100
and CDMSlite. We find these experiments to disfavor previously allowed
parameter space. Moreover, we derive sensitivity projections for SuperCDMS at
SNOLAB for silicon and germanium targets, as well as for various possible
experiments with scintillating targets (cesium iodide, sodium iodide, and
gallium arsenide). The projected sensitivity can probe large new regions of
parameter space. For axion-like particles, the same current direction detection
data improves on previously known direct-detection constraints but does not
bound new parameter space beyond known stellar cooling bounds. However,
projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go
beyond these and even probe parameter space consistent with possible hints from
the white dwarf luminosity function. We find similar results for dark photons
from the sun. For all cases, direct-detection experiments can have
unprecedented sensitivity to dark-sector particles.Comment: 18 pages, 5 figures, Figs. 3 and 4 fixed, appendices adde
Solar Neutrinos as a Signal and Background in Direct-Detection Experiments Searching for Sub-GeV Dark Matter With Electron Recoils
Direct-detection experiments sensitive to low-energy electron recoils from
sub-GeV dark matter (DM) interactions will also be sensitive to solar neutrinos
via coherent neutrino-nucleus scattering (CNS), since the recoiling nucleus can
produce a small ionization signal. Solar neutrinos constitute both an
interesting signal in their own right and a potential background to a DM search
that cannot be controlled or reduced by improved shielding, material
purification and handling, or improved detector design. We explore these two
possibilities in detail for semiconductor (Si and Ge) and Xe targets,
considering several possibilities for the unmeasured ionization efficiency at
low energies. For DM-electron-scattering searches, neutrinos start being an
important background for exposures larger than ~1-10 kg-years in Si and Ge, and
for exposures larger than ~0.1-1 kg-year in Xe. For the absorption of bosonic
DM (dark photons and axion-like particles) by electrons, neutrinos are most
relevant for masses below ~1 keV and again slightly more important in Xe.
Treating the neutrinos as a signal, we find that the CNS of B-8 neutrinos can
be observed with ~2 sigma significance with exposures of ~2, 7, and 20 kg-years
in Xe, Ge, and Si, respectively, assuming there are no other backgrounds. We
give an example for how this would constrain non-standard neutrino
interactions. Neutrino components at lower energy can only be detected if the
ionization efficiency is sufficiently large. In this case, observing pep
neutrinos via CNS requires exposures ~10-100 kg-years in Si or Ge (~1000
kg-years in Xe), and observing CNO neutrinos would require an order of
magnitude more exposure. Only Si could potentially detect Be-7 neutrinos. These
measurements would allow for a direct measurement of the electron-neutrino
survival probability over a wide energy range.Comment: 17 pages + refs, 15 figures, 4 tables. v3 minor corrections. Scaling
of Fig. 9 corrected. Minor corrections to Fig. 4,7,8 and 15. Conclusions
unchange
BBN constraints on universally-coupled ultralight scalar dark matter
Ultralight scalar dark matter can interact with all massive Standard Model
particles through a universal coupling. Such a coupling modifies the Standard
Model particle masses and affects the dynamics of Big Bang Nucleosynthesis. We
model the cosmological evolution of the dark matter, taking into account the
modifications of the scalar mass by the environment as well as the full
dynamics of Big Bang Nucleosynthesis. We find that precision measurements of
the helium-4 abundance set stringent constraints on the available parameter
space, and that these constraints are strongly affected by both the dark matter
environmental mass and the dynamics of the neutron freeze-out. Furthermore, we
perform the analysis in both the Einstein and Jordan frames, the latter of
which allows us to implement the model into numerical Big Bang Nucleosynthesis
codes and analyze additional light elements. The numerical analysis shows that
the constraint from helium-4 dominates over deuterium, and that the effect on
lithium is insufficient to solve the lithium problem. Comparing to several
other probes, we find that Big Bang Nucleosynthesis sets the strongest
constraints for the majority of the parameter space.Comment: 23 pages + appendices and bibliography, 6 figures, v2: typos
corrected, expanded discussion around eq. 4.5, published versio
Constraints on Ultralight Scalar Dark Matter with Quadratic Couplings
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 bath, which affects
the cosmological evolution of the dark matter. Secondly, we treat the weak
freeze-out using the full kinetic equations instead of using an instantaneous
approximation. Both improvements were shown to impact the Helium-4 prediction
in the context of universally-coupled dark matter in previous work. We extend
these lessons to more general couplings. We show that with these modifications,
Big Bang Nucleosynthesis provides strong constraints of ultralight dark matter
with quadratic couplings to the Standard Model for a large range of masses as
compared to other probes of this model, such as equivalence principle tests,
atomic and nuclear clocks, as well as astrophysical and other cosmological
probes.Comment: 16 pages, 3 figure
Direct Detection of sub-GeV Dark Matter with Semiconductor Targets
Dark matter in the sub-GeV mass range is a theoretically motivated but
largely unexplored paradigm. Such light masses are out of reach for
conventional nuclear recoil direct detection experiments, but may be detected
through the small ionization signals caused by dark matter-electron scattering.
Semiconductors are well-studied and are particularly promising target materials
because their band gaps allow for ionization signals from
dark matter as light as a few hundred keV. Current direct detection
technologies are being adapted for dark matter-electron scattering. In this
paper, we provide the theoretical calculations for dark matter-electron
scattering rate in semiconductors, overcoming several complications that stem
from the many-body nature of the problem. We use density functional theory to
numerically calculate the rates for dark matter-electron scattering in silicon
and germanium, and estimate the sensitivity for upcoming experiments such as
DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has
the potential to be orders of magnitude beyond current direct detection
constraints and that sub-GeV dark matter has a sizable modulation signal. We
also give the first direct detection limits on sub-GeV dark matter from its
scattering off electrons in a semiconductor target (silicon) based on published
results from DAMIC. We make available publicly our code, QEdark, with which we
calculate our results. Our results can be used by experimental collaborations
to calculate their own sensitivities based on their specific setup. The
searches we propose will probe vast new regions of unexplored dark matter model
and parameter space.Comment: 30 pages + 22 pages appendices/references, 17 figures, website at
http://ddldm.physics.sunysb.edu/, v2 added references, minor edits to text
and Figs. 2 and 14, version to appear in JHE
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