We present a novel study on the problem of constructing mass
models for the Milky Way, concentrating on features regarding the
dark matter halo component. We have considered a variegated sample
of ...dynamical observables for the Galaxy, including several results
which have appeared recently, and studied a 7- or 8-dimensional
parameter space - defining the Galaxy model - by implementing a
Bayesian approach to the parameter estimation based on a Markov
Chain Monte Carlo method. The main result of this analysis is a
novel determination of the local dark matter halo density which,
assuming spherical symmetry and either an Einasto or an NFW density
profile is found to be around 0.39 GeV cm
−3
with a 1-σ
error bar of about 7%; more precisely we find a ρ
DM
(
R
0
) = 0.385±0.027 GeV cm
−3
for the Einasto profile and
ρ
DM
(
R
0
) = 0.389±0.025 GeV cm
−3
for the
NFW. This is in contrast to the standard assumption that
ρ
DM
(
R
0
) is about 0.3 GeV cm
−3
with an uncertainty of a
factor of 2 to 3. A very precise determination of the local halo
density is very important for interpreting direct dark matter
detection experiments. Indeed the results we produced, together with
the recent accurate determination of the local circular velocity,
should be very useful to considerably narrow astrophysical
uncertainties on direct dark matter detection.
Direct detection experiments search for the interactions of Dark Matter (DM) particles with nuclei in terrestrial detectors. But if these interactions are sufficiently strong, DM particles may ...scatter in the Earth, affecting their distribution in the lab. We present a new analytic calculation of this 'Earth-scattering' effect in the regime where DM particles scatter at most once before reaching the detector. We perform the calculation self-consistently, taking into account not only those particles which are scattered away from the detector, but also those particles which are deflected towards the detector. Taking into account a realistic model of the Earth and allowing for a range of DM-nucleon interactions, we present the EARTHSHADOW code, which we make publicly available, for calculating the DM velocity distribution after Earth-scattering. Focusing on low-mass DM, we find that Earth-scattering reduces the direct detection rate at certain detector locations while increasing the rate in others. The Earth's rotation induces a daily modulation in the rate, which we find to be highly sensitive to the detector latitude and to the form of the DM-nucleon interaction. These distinctive signatures would allow us to unambiguously detect DM and perhaps even identify its interactions in regions of the parameter space within the reach of current and future experiments.
In the leading paradigm of modern cosmology, about 80% of our Universe's matter content is in the form of hypothetical, as yet undetected particles. These do not emit or absorb radiation at any ...observable wavelengths, and therefore constitute the so-called dark matter (DM) component of the Universe. Detecting the particles forming the Milky Way DM component is one of the main challenges for astroparticle physics and basic science in general. One promising way to achieve this goal is to search for rare DM-electron interactions in low-background deep underground detectors. Key to the interpretation of this search is the response of detectors' materials to elementary DM-electron interactions defined in terms of electron wave functions' overlap integrals. In this work, we compute the response of atomic argon and xenon targets used in operating DM search experiments to general, so far unexplored DM-electron interactions. We find that the rate at which atoms can be ionized via DM-electron scattering can in general be expressed in terms of four independent atomic responses, three of which we identify here for the first time. We find our new atomic responses to be numerically important in a variety of cases, which we identify and investigate thoroughly using effective theory methods. We then use our atomic responses to set 90% confidence level (C.L.) exclusion limits on the strength of a wide range of DM-electron interactions from the null result of DM search experiments using argon and xenon targets.
We present a new determination of the local dark matter phase-space density. This result is obtained implementing, in the limit of isotropic velocity distribution and spherical symmetry, Eddington's ...inversion formula, which links univocally the dark matter distribution function to the density profile, and applying, within a Bayesian framework, a Markov Chain Monte Carlo algorithm to sample mass models for the Milky Way against a broad and variegated sample of dynamical constraints. The derived dark matter phase-space densities differ significantly - most dramatically in the high velocity tails - from the model usually taken as a reference in dark matter detection studies, a Maxwell-Boltzmann distribution with velocity dispersion fixed in terms of the local circular velocity and with a sharp truncation at a given value of the escape velocity. Tools for applying our result on the local dark matterphase-space density to other dark matter candidates or experimental setups arc provided.
We combine the nonrelativistic effective theory of dark matter (DM)-electron interactions with linear response theory to obtain a formalism that fully accounts for screening and collective ...excitations in DM-induced electronic transition rate calculations for general DM-electron interactions. In the same way that the response of a dielectric material to an external electric field in electrodynamics is described by the dielectric function, so in our formalism the response of a detector material to a DM perturbation is described by a set of which can be directly related to densities and currents arising from the nonrelativistic expansion of the Dirac Hamiltonian. We apply our formalism to assess the sensitivity of non-spin-polarized detectors, and find that in-medium effects significantly affect the experimental sensitivity if DM couples to the detector's electron density, while being decoupled from other densities and currents. Our formalism can be straightforwardly extended to the case of spin-polarized materials. Published by the American Physical Society 2024
A
bstract
We investigate the non-relativistic reduction of simplified models for spin 1 dark matter (DM) with the aim of identifying features in the phenomenology of DM-quark interactions which are ...specific to vector DM. In the case of DM-quark interactions mediated by a spin 1 particle, we find two DM-nucleon interaction operators arising from the non-relativistic reduction of simplified models for spin 1 DM that are specific to spin 1 DM, and which were not considered in previous studies. They are quadratic in the momentum transfer, linear in a symmetric combination of polarisation vectors for the DM particle, and arise from simplified models which do not generate momentum transfer independent operators as leading interactions in the non-relativistic expansion of DM-nucleon scattering amplitudes. Within these simplified models, the new operators cannot be neglected when computing DM signals at direct detection experiments. For example, we find that nuclear recoil energy spectra computed by including or neglecting the new operators can differ by up to one order of magnitude for nuclear recoil energies larger than about 20 keV and DM masses below 50 GeV. Furthermore, the shape of the expected nuclear recoil spectra depends significantly on whether the new operators are taken into account or not. Finally, neglecting the contribution to DM direct detection signals from the new operators leads to inaccurate conclusions when assessing the compatibility of a future direct detection signal with CMB constraints on the DM relic density, especially when the number of signal events is small, e.g.
O
(1).
Dark matter N-body simulations suggest that the velocity distribution of dark matter is anisotropic. In this work we employ a mass model for the Milky Way whose parameters are determined from a fit ...to kinematical data. Then we adopt an ansatz for the dark matter phase space distribution which allows to construct self-consistent halo models which feature a degree of anisotropy as a function of the radius such as suggested by the simulations. The resulting velocity distributions are then used for an analysis of current data from dark matter direct detection experiments. We find that velocity distributions which are radially biased at large galactocentric distances (up to the virial radius) lead to an increased high velocity tail of the local dark matter distribution. This affects the interpretation of data from direct detection experiments, especially for dark matter masses around 10 GeV, since in this region the high velocity tail is sampled. We find that the allowed regions in the dark matter mass-cross section plane as indicated by possible hints for a dark matter signal reported by several experiments as well as conflicting exclusion limits from other experiments shift in a similar way when the halo model is varied. Hence, it is not possible to improve the consistency of the data by referring to anisotropic halo models of the type considered in this work.
A
bstract
It is well-known that dark matter (DM) direct detection experiments and the LHC are complementary, since they probe physical processes occurring at different energy scales. And yet, there ...are aspects of this complementarity which are still not fully understood, or exploited. For example, what is the impact that the discovery of DM at XENONnT would have on present and future searches for DM in LHC final states involving a pair of hadronic jets? In this work we investigate the impact of a XENONnT signal on the interpretation of current dijet searches at the LHC, and on the prospects for dijet signal discovery at the High-Luminosity (HL) LHC in the framework of simplified models. Specifically, we focus on a general class of simplified models where DM can have spin 0, 1/2 or 1, and interacts with quarks through the exchange of a scalar, pseudo-scalar, vector, or pseudo-vector mediator. We find that exclusion limits on the mediator’s mass and its coupling to quarks from dijet searches at the LHC are significantly affected by a signal at XENONnT, and that
O
(100) signal events at XENONnT would drastically narrow the region in the parameter space of simplified models where a dijet signal can be discovered at 5
σ
C.L. at the HL-LHC.
We develop a formalism to describe the scattering of dark matter (DM) particles by electrons bound in crystals for a general form of the underlying DM-electron interaction. Such a description is ...relevant for direct-detection experiments of DM particles lighter than a nucleon, which might be observed in operating DM experiments via electron excitations in semiconductor crystal detectors. Our formalism is based on an effective theory approach to general nonrelativistic DM-electron interactions, including the anapole, and magnetic and electric dipole couplings, combined with crystal response functions defined in terms of electron wave function overlap integrals. Our main finding is that, for the usual simplification of the velocity integral, the rate of DM-induced electronic transitions in a semiconductor material depends on at most five independent crystal response functions four of which are distinct from the usual scalar response. We identify these crystal responses and evaluate them using density functional theory for crystalline silicon and germanium, which are used in operating DMdirect-detection experiments. Our calculations allow us to set 90% confidence level limits on the strength of DM-electron interactions from data reported by the SENSEI and EDELWEISS experiments. The crystal response functions discovered in this paper encode properties of crystalline solids that do not interact with conventional experimental probes, suggesting the use of the DM wind as a probe to reveal new kinds of hidden order in materials.
We extend the formalism of dark matter directional detection to arbitrary one-body dark matter-nucleon interactions. The new theoretical framework generalizes the one currently used, which is based ...on 2 types of dark matter-nucleon interaction only. It includes 14 dark matter-nucleon interaction operators, 8 isotope-dependent nuclear response functions, and the Radon transform of the first 2 moments of the dark matter velocity distribution. We calculate the recoil energy spectra at dark matter directional detectors made of CF{sub 4}, CS{sub 2} and {sup 3}He for the 14 dark matter-nucleon interactions, using nuclear response functions recently obtained through numerical nuclear structure calculations. We highlight the new features of the proposed theoretical framework, and present our results for a spherical dark matter halo and for a stream of dark matter particles. This study lays the foundations for model independent analyses of dark matter directional detection experiments.
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