25 research outputs found
Curl up with a good : Detecting ultralight dark matter with differential magnetometry
Ultralight dark matter (such as kinetically mixed dark-photon dark matter or
axionlike dark matter) can source an oscillating magnetic-field signal at the
Earth's surface, which can be measured by a synchronized array of ground-based
magnetometers. The global signal of ultralight dark matter can be robustly
predicted for low masses, when the wavelength of the dark matter is larger than
the radius of the Earth, . However, at higher masses,
environmental effects, such as the Schumann resonances, can become relevant,
making the global magnetic-field signal difficult to reliably
model. In this work, we show that is robust to global
environmental details, and instead only depends on the local dark matter
amplitude. We therefore propose to measure the local curl of the magnetic field
at the Earth's surface, as a means for detecting ultralight dark matter with
. As this measurement requires vertical
gradients, it can be done near a hill/mountain. Our measurement scheme not only
allows for a robust prediction, but also acts as a background rejection scheme
for external noise sources. We show that our technique can be the most
sensitive terrestrial probe of dark-photon dark matter for frequencies
(corresponding to masses
). It
can also achieve sensitivities to axionlike dark matter comparabe to the CAST
helioscope, in the same frequency range.Comment: 16 pages, 3 figure
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
Noise Injection Node Regularization for Robust Learning
We introduce Noise Injection Node Regularization (NINR), a method of
injecting structured noise into Deep Neural Networks (DNN) during the training
stage, resulting in an emergent regularizing effect. We present theoretical and
empirical evidence for substantial improvement in robustness against various
test data perturbations for feed-forward DNNs when trained under NINR. The
novelty in our approach comes from the interplay of adaptive noise injection
and initialization conditions such that noise is the dominant driver of
dynamics at the start of training. As it simply requires the addition of
external nodes without altering the existing network structure or optimization
algorithms, this method can be easily incorporated into many standard problem
specifications. We find improved stability against a number of data
perturbations, including domain shifts, with the most dramatic improvement
obtained for unstructured noise, where our technique outperforms other existing
methods such as Dropout or regularization, in some cases. We further show
that desirable generalization properties on clean data are generally
maintained.Comment: 16 pages, 9 figure
Axion-like Relics: New Constraints from Old Comagnetometer Data
The noble-alkali comagnetometer, developed in recent years, has been shown to
be a very accurate measuring device of anomalous magnetic-like fields. An
ultra-light relic axion-like particle can source an anomalous field that
permeates space, allowing for its detection by comagnetometers. Here we derive
new constraints on relic axion-like particles interaction with neutrons and
electrons from old comagnetometer data. We show that the decade-old
experimental data place the most stringent terrestrial constraints to date on
ultra-light axion-like particles coupled to neutrons. The constraints are
comparable to those from stellar cooling, providing a complementary probe.
Future planned improvements of comagnetometer measurements through altered
geometry, constituent content and data analysis techniques could enhance the
sensitivity to axion-like relics coupled to nucleons or electrons by many
orders of magnitude.Comment: 20 pages, 3 figures, 2 table
Crunching Away the Cosmological Constant Problem: Dynamical Selection of a Small
We propose a novel explanation for the smallness of the observed cosmological
constant (CC). Regions of space with a large CC are short lived and are
dynamically driven to crunch soon after the end of inflation. Conversely,
regions with a small CC are metastable and long lived and are the only ones to
survive until late times. While the mechanism assumes many domains with
different CC values, it does not result in eternal inflation nor does it
require a long period of inflation to populate them. We present a concrete
dynamical model, based on a super-cooled first order phase transition in a
hidden conformal sector, that may successfully implement such a crunching
mechanism. We find that the mechanism can only solve the CC problem up to the
weak scale, above which new physics, such as supersymmetry, is needed to solve
the CC problem all the way to the UV cutoff scale. The absence of experimental
evidence for such new physics already implies a mild little hierarchy problem
for the CC. Curiously, in this approach the weak scale arises as the geometric
mean of the temperature in our universe today and the Planck scale, hinting on
a new "CC miracle", motivating new physics at the weak scale independent of
electroweak physics. We further predict the presence of new relativistic
degrees of freedom in the CFT that should be visible in the next round of CMB
experiments. Our mechanism is therefore experimentally falsifiable and
predictive
SENSEI: Characterization of Single-Electron Events Using a Skipper-CCD
We use a science-grade Skipper Charge Coupled Device (Skipper-CCD) operating
in a low-radiation background environment to develop a semi-empirical model
that characterizes the origin of single-electron events in CCDs. We identify,
separate, and quantify three independent contributions to the single-electron
events, which were previously bundled together and classified as ``dark
counts'': dark current, amplifier light, and spurious charge. We measure a dark
current, which depends on exposure, of (5.89+-0.77)x10^-4 e-/pix/day, and an
unprecedentedly low spurious charge contribution of (1.52+-0.07)x10^-4 e-/pix,
which is exposure-independent. In addition, we provide a technique to study
events produced by light emitted from the amplifier, which allows the
detector's operation to be optimized to minimize this effect to a level below
the dark-current contribution. Our accurate characterization of the
single-electron events allows one to greatly extend the sensitivity of
experiments searching for dark matter or coherent neutrino scattering.
Moreover, an accurate understanding of the origin of single-electron events is
critical to further progress in ongoing R&D efforts of Skipper and conventional
CCDs.Comment: 9 pages, 6 figures, 4 table
Exploring New Physics with O(keV) Electron Recoils in Direct Detection Experiments
Motivated by the recent XENON1T results, we explore various new physics models that can be discovered through searches for electron recoils in O(keV)-threshold direct-detection experiments. First, we consider the absorption of light bosons, either as dark matter relics or being produced directly in the Sun. In the latter case, we find that keV mass bosons produced in the Sun provide an adequate fit to the data but are excluded by stellar cooling constraints. We address this tension by introducing a novel Chameleon-like axion model, which can explain the excess while evading the stellar bounds. We find that absorption of bosonic dark matter provides a viable explanation for the excess only if the dark matter is a dark photon or an axion. In the latter case, photophobic axion couplings are necessary to avoid X-ray constraints. Second, we analyze models of dark matter-electron scattering to determine which models might explain the excess. Standard scattering of dark matter with electrons is generically in conflict with data from lower-threshold experiments. Momentum-dependent interactions with a heavy mediator can fit the data with dark matter mass heavier than a GeV but are generically in tension with collider constraints. Next, we consider dark matter consisting of two (or more) states that have a small mass splitting. The exothermic (down)scattering of the heavier state to the lighter state can fit the data for keV mass splittings. Finally, we consider a subcomponent of dark matter that is accelerated by scattering off cosmic rays, finding that dark matter interacting though an O(100 keV)-mass mediator can fit the data. The cross sections required in this scenario are, however, typically challenged by complementary probes of the light mediator. Throughout our study, we implement an unbinned Monte Carlo analysis and use an improved energy reconstruction of the XENON1T events
New constraints on axion-like dark matter using a Floquet quantum detector
Dark matter is one of the greatest mysteries in physics. It interacts via gravity and composes most of our universe, but its elementary composition is unknown. We search for nongravitational interactions of axion-like dark matter with atomic spins using a precision quantum detector. The detector is composed of spin-polarized xenon gas that can coherently interact with a background dark matter field as it traverses through the galactic dark matter halo. Conducting a 5-month-long search, we report on the first results of the Noble and Alkali Spin Detectors for Ultralight Coherent darK matter (NASDUCK) collaboration. We limit ALP-neutron interactions in the mass range of 4 × 10-15 to 4 × 10-12 eV/c2 and improve upon previous terrestrial bounds by up to 1000-fold for masses above 4 × 10-13 eV/c2. We also set bounds on pseudoscalar dark matter models with quadratic coupling