The mathematical expression for the dark matter nuclear recoil event rate in a detector consists of a six-dimensional integral over the velocity distribution of dark matter in the detector frame and over the recoil momentum of the nucleus. While a significant part of this integral can be solved in closed form under traditional assumptions of the standard halo model and/or isotropic detector response, analysis of alternate assumptions is conventionally impeded by the inefficiency of multidimensional numerical integration methods. In this work, we introduce a novel, fast, and efficient algorithm for direct detection event rate computations. This algorithm takes advantage of a closed-form expression for the Radon transform of three-dimensional Zernike functions, which are used as basis functions for the velocity distribution. We demonstrate an implementation of this algorithm zebradm, which is typically faster than an optimized numerical integration approach by a factor between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mn>4</mn></msup></math>.

Finland

Sebastian Sassi

Aula Al-Adulrazzaq

Matti Heikinheimo

Kimmo Tuominen

Fast numerical evaluation of dark matter direct detection event rates

We consider constraints on the axion-photon coupling by superradiance due to a plasma instability in the magnetospheres of millisecond pulsars. We compute the growth rate of a superradiant axion cloud in a dipole magnetic field, and give a semianalytical formula for the superradiance rate for the lowest state. By requiring the associated instability time to be longer than the characteristic age of the supermassive black-widow millisecond pulsar PSR J0952-0607, we examine the pulsar-timing array constraints on axions of mass <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>12</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math>. We find that competitive axion bounds from plasma instabilities are unlikely unless a new high spin pulsar is discovered.

Topi Sirkiä

Axion superradiance in dipole magnetic fields of pulsars

We consider dark matter velocity distributions with an anisotropic component, and analyze how the velocity structure can be probed in a solid-state ionization detector with no directional detection capability using a daily modulation effect due to the anisotropic response function of the target. We show that with an energy resolution of <math><mo>&lt;</mo><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi></math> it is possible to identify the presence of an anisotropic component consistent with observations for sub-GeV dark matter, and that introduction of daily modulation information substantially improves the sensitivity in a narrow mass range.

Kai Nordlund

Probing the dark matter velocity distribution via daily modulation

We study the origin of the real intermediate state subtraction problem and compare its different solutions. We show that the ambiguity in subtraction schemes arises from the on-shell approximation for the 2-point functions that reduces the Schwinger-Dyson equations to the Boltzmann limit. We also suggest a new subtraction scheme which, unlike the earlier definitions, never leads to negative scattering rates. This scheme also quantifies the validity of the on-shell limit in terms of an effective one-particle weight function <math><mi>R</mi><mo>(</mo><mi>Δ</mi><mo>)</mo></math>, where <math><mi>Δ</mi></math> measures the region around the resonance associated with the real state.

Kalle Ala-Mattinen

Kimmo Kainulainen

Anatomy of real intermediate state-subtraction scheme

We study possible strong first-order electroweak phase transitions in Composite Higgs models and we quantify the part of parameter space that can be probed with future gravitational wave experiments. We focus on models where the Composite Higgs sector arises from underlying four-dimensional strongly interacting gauge theories with fermions, and where the Standard Model fermion masses are induced via linear mixing terms with composite fermions — the so-called fermion partial compositeness framework. We perform our analysis for the general class of Composite Higgs models arising from N Weyl fermions in a pseudo-real representation of the new strongly interacting gauge group that dynamically triggers the global chiral symmetry breaking pattern SU(N) → Sp(N). The minimal model has N = 4 and for N &gt; 4 the models feature complex scalar dark matter candidates arising as pseudo-Nambu-Goldstone bosons. We find a large number of points in the models parameter space which yield strong first-order electroweak phase transitions and identify the most important operators characterizing the strength of the phase transition. Almost all of these points are testable with future GW detectors such as LISA, Taiji, Tianqin, BBO, DECIGO and Ultimate-DECIGO.

Denmark

Mads Frandsen

United Kingdom

Martin Rosenlyst

Mattias Thing

Gravitational waves from SU(N)/SP(N) composite Higgs models

We consider extensions of the Standard Model by a hidden sector consisting of a gauge field coupled with a scalar field. In the absence of dimensionful parameters in the tree-level potential, radiative symmetry breaking will induce the electroweak scale of the Standard Model and generate mass for the hidden sector gauge field. We consider both <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>D</mi></msub></math> and <math><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><msub><mo>)</mo><mi>D</mi></msub></math> dark sector gauge groups and focus on probing the models with a combination of direct detection experiments and gravitational wave observatories. We find that recent dark matter direct detection results significantly constrain the parameter space of the models where they can account for the observed dark matter relic density via freeze-out. The gravitational wave signals originating from strongly first-order electroweak phase transition in these models can be probed in future gravitational wave observatories such as the Laser Interferometer Space Antenna. We show how the projected results complement direct detection experiments and can help probe parameter space near the neutrino floor of direct detection.

Mads T. Frandsen

Mattias E. Thing

Vector dark matter in supercooled Higgs portal models

An excess of events of unknown origin at low energies below 1 keV has been observed in multiple low-threshold dark matter detectors. Understanding the origin of these events is of utmost importance, as this unidentified event rate currently overwhelms any potential new physics signal. Depending on the target material, nuclear recoil events at these energies may cause lattice defects, in which case a part of the true recoil energy is stored in the defect and not observed in the phonon detector. If the threshold for defect creation is sharp, this effect leads to a prominent feature in the observed recoil spectrum. Electronic recoils at low energies do not create defects and therefore the feature in the observed spectrum is not expected in that case. We propose to use the sharp defect creation threshold of diamond to test if the low-energy events are due to nuclear recoils. Based on simulated data we expect the nuclear recoil peak in the observed spectrum to be visible in diamond with a data set of <math><mo>∼</mo><mn>700</mn></math> events, potentially achievable with <math><mo>∼</mo><mn>0.1</mn></math> gram days of exposure.

United States

Nader Mirabolfathi

Identification of the low-energy excess in dark matter searches with crystal defects

SU(2) gauge theory with <math><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>=</mo><mn>24</mn></mrow></math> massless fermions is noninteracting at long distances, i.e., it has an infrared fixed point at vanishing coupling. With massive fermions, the fermions are expected to decouple at energy scales below the fermion mass, and the infrared behavior is that of confining SU(2) pure gauge theory. We demonstrate this behavior nonperturbatively with lattice Monte Carlo simulations by measuring the gradient flow running coupling.

Switzerland

Tobias Rindlisbacher

Kari Rummukainen

Ahmed Salami

Nonperturbative Decoupling of Massive Fermions

Recent progress in phonon-mediated detectors with eV-scale nuclear recoil energy sensitivity requires an understanding of the effect of the crystalline defects on the energy spectrum expected from dark matter or neutrino coherent scattering. We perform molecular dynamics simulations to determine the amount of energy stored in the lattice defects as a function of the recoil direction and energy. This energy cannot be observed in the phonon measurement, thus affecting the observed energy spectrum compared to the underlying true recoil energy spectrum. We describe this effect for multiple commonly used detector materials and demonstrate how the predicted energy spectrum from dark matter scattering is modified.

Antti Kuronen

Jesper Byggmästar

Energy loss in low energy nuclear recoils in dark matter detector materials

We solve coupled momentum-dependent Boltzmann equations for the phase space distribution of cosmic relic particles, without resorting to approximations of assuming kinetic equilibrium or neglecting backscattering or elastic interactions. Our method is amendable to precision numerical computations. To test it, we consider two benchmark models where the momentum dependence of dark matter distribution function is potentially important: a real singlet scalar extension near the Higgs resonance and a sterile neutrino dark matter model with a singlet scalar mediator. The singlet scalar example shows that the kinetic equilibrium may hold surprisingly well even near sharp resonances. However, the integrated method may underestimate the relic density by up to 40% in extreme cases. In the sterile neutrino dark matter model, we studied how the inclusion of previously ignored elastic interactions and processes with initial state sterile neutrinos could affect the nonthermal nature of their resulting distributions. Here the effects turned out to be negligible, proving the robustness of the earlier predictions.