Axionlike particles and similar new pseudoscalar as well as vector bosons coupled to nucleons and electrons are predicted to lead to spin-dependent forces in atoms and ions. We argue that hyperfine structure measurements in hydrogenlike and lithiumlike charge states are a sensitive probe to this effect. Employing specific differences of these splittings reduces uncertainties due to nuclear effects in hyperfine structure calculations and measurements. Using this, we show that existing measurements on Be provide competitive limits in the region <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>≳</mo><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></mrow></math>, confirming, or improving by up to a factor of 2, existing constraints for pseudoscalar couplings, depending on the nuclear model. We also find that future measurements on Cs have a further factor of 2-2.5 improved discovery potential for pseudoscalars and an order of magnitude for new vector bosons when compared with the corresponding current constraints.

Germany

Cedric Quint

Fabian Heiße

Joerg Jaeckel

Lutz Leimenstoll

Christoph H. Keitel

Zoltán Harman

Stringent Constraints on New Pseudoscalar and Vector Bosons from Precision Hyperfine Splitting Measurements

Wavelike dark matter may feature quadratic couplings to ordinary matter. This carries profound consequences for the phenomenologies of such models. It changes the dark matter density around dense objects made from ordinary matter such as planets and stars, thereby changing the sensitivity of direct detection experiments on Earth as well as implying forces on other ordinary matter objects in the vicinity. In this paper we study the time dependence of the dark matter field around spherical objects of ordinary matter. This work indicates the timescale on which accelerating objects settle into a stationary state and delineates the applicability of stationary solutions for experimental dark matter tests. We also use this to understand (and effectively eliminate) the infinities in energies, forces, and pressures that appear when naively comparing the total energy around objects with different size but the same total number of ordinary matter particles.

United Kingdom

Clare Burrage

Benjamin Elder

Australia

Yeray Garcia del Castillo

Time-dependent density of quadratically coupled dark matter around ordinary matter objects

In quantum field theories, field redefinitions are often employed to remove redundant operators in the Lagrangian, making calculations simpler and physics more evident. This technique requires some care regarding, among other things, the choice of observables, the range of applicability, and the appearance and disappearance of solutions of the equations of motion (EOM). Many of these issues can already be studied at the classical level, which is the focus of this work. We highlight the importance of selecting appropriate observables and initial/boundary conditions to ensure the physical invariance of solutions. A classical analog to the Lehmann-Symanzik-Zimmermann (LSZ) formula is presented, confirming that some observables remain independent of field variables without tracking redefinitions. Additionally, we address, with an example, the limitations of noninvertible field redefinitions, particularly with nonperturbative objects like solitons, and discuss their implications for classical and quantum field theories.

Spain

Juan Carlos Criado

Michael Spannowsky

Field redefinitions in classical field theory with some quantum perspectives

Ordinary matter coupled to light weakly interacting bosons can lead to the formation of a macroscopic bosonic field in the vicinity of large matter concentrations such as ordinary or neutron stars. When these objects are turned into black holes due to a supernova or a binary merger this “hair” could be “shorn” off. Part of the field configuration would then be released leading to an outgoing field wave. For small masses this field transient remains rather compact and can induce a transient signal in experiments, in particular those that look for wave-like dark matter. This signal can be correlated with the corresponding astrophysical signal of the event. In this note, we consider a variety of couplings and the associated signals and estimate the corresponding sensitivities.

Arturo Giorgi

Star shearing season: transient signals in wave-like dark matter experiments from black hole formation

Establishing the axion as the dark matter (DM) particle after a haloscope discovery typically requires follow-up experiments to break the degeneracy between the axion’s coupling to photons and its local DM abundance. Given that a discovery would justify more significant investments, we explore the prospects of ambitious light-shining-through-a-wall (LSW) setups to probe the QCD axion band. Leveraging the excellent mass determination in haloscopes, we show how to design LSW experiments with lengths on the order of 100 km and suitably aligned magnetic fields with apertures of around 1 m to reach well-motivated axion models across up to four orders of magnitude in mass. Beyond presenting a concrete plan for postdiscovery experimental efforts, we briefly discuss complementary experiments and future directions beyond LSW experiments.

Italy

Sebastian Hoof

Giuseppe Lucente

Ultimate light-shining-through-a-wall experiments to establish QCD axions as the dominant form of dark matter

Dark photons in the MeV to GeV range with kinetic mixing of the order of ≲ 10 −4 − 10 −3 can be produced in significant numbers at low energy colliders such as Belle II. Their decay length can be macroscopic raising the hope for a fairly clean search via displaced vertices as proposed in [1]. However, even this is not background free. Here, we calculate and discuss problematic backgrounds from displaced photon conversion and discuss their potential impact on the sensitivity. In addition we also briefly consider the dangers of prompt backgrounds.

Netherlands

Anh Phan

Searching dark photons using displaced vertices at Belle II — with backgrounds

Kinetic mixing between gauge fields of different U(1) factors is a well-studied phenomenon in 4d EFT. In string compactifications with U(1)s from sequestered D-brane sectors, kinetic mixing becomes a key target for the UV prediction of a phenomenologically important EFT operator. Surprisingly, in many cases kinetic mixing is absent due to a non-trivial cancellation. In particular, D3-D3 kinetic mixing in type-IIB vanishes while D3-anti-D3 mixing does not. This follows both from exact CFT calculations on tori as well as from a leading-order 10d supergravity analysis, where the key cancellation is between the C 2 and B 2 contribution. We take the latter approach, which is the only one available in realistic Calabi-Yau settings, to a higher level of precision by including sub-leading terms of the brane action and allowing for non-vanishing C 0. The exact cancellation persists, which we argue to be the result of  $${\text{SL}}\left(2,{\mathbb{R}}\right)$$  self-duality. We note that a B 2 C 2 term on the D3-brane, which is often missing in the recent literature, is essential to obtain the correct zero result. Finally, allowing for  $${\text{SL}}\left(2,{\mathbb{R}}\right)$$ -breaking fluxes, kinetic mixing between D3-branes arises at a volume-suppressed level. We provide basic explicit formulae, both for kinetic as well as magnetic mixing, leaving the study of phenomenologically relevant, more complex situations for the future. We also note that describing our result in 4d supergravity appears to require higher-derivative terms — an issue which deserves further study.

Arthur Hebecker

Ruben Kuespert

Small kinetic mixing in string theory

We note the possibility to perform a parametrically improved search for gauged baryon (B) and baryon minus lepton (<math><mi>B</mi><mo>−</mo><mi>L</mi></math>) Dark Photon Dark Matter (DPDM) using auxiliary channel data from LISA Pathfinder. In particular we use the measurement of the differential movement between the test masses (TMs) and the space craft (SC) which is nearly as sensitive as the tracking between the two TMs. TMs and SC are made from different materials and therefore have different charge-to-mass ratios for both <math><mi>B</mi><mo>−</mo><mi>L</mi></math> and B. Thus, the surrounding DPDM field induces a relative acceleration of nearly constant frequency. For the case of <math><mi>B</mi><mo>−</mo><mi>L</mi></math>, we find that LISA Pathfinder can constrain previously unexplored parameter space, providing the world leading limits in the mass range <math><mn>4</mn><mo>⋅</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>19</mn></mrow></msup><mspace width="0.25em"></mspace><mtext>eV</mtext><mo>&lt;</mo><mi>m</mi><mo>&lt;</mo><mn>3</mn><mo>⋅</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>17</mn></mrow></msup><mspace width="0.25em"></mspace><mtext>eV</mtext></math>. This limit can easily be recast also for dark photons that arise from gauging other global symmetries of the SM.

Jonas Frerick

Felix Kahlhoefer

Kai Schmidt-Hoberg

Riding the dark matter wave: Novel limits on general dark photons from LISA Pathfinder

Time and space translation invariance, giving rise to energy and momentum conservation, are not only amongst the most fundamental but also the most generally accepted symmetry assumptions in physics. It is nevertheless prudent to put such assumptions to experimental and observational tests. In this note, we take the first step in this direction, specifying a simple periodic time dependence that violates time translation invariance in QED, and setting phenomenological constraints on it. In addition to observational and experimental constraints on time varying couplings, we focus on probes of violation of energy conservation such as spontaneous production of photon and electron pairs and the e → eγ process. We discuss similarities and differences to the discussion of time varying fundamental constants and to the case of a light bosonic dark matter field that usually also causes oscillating effects.

India

Rick Gupta

Probing Poincaré violation

We discuss baryogenesis in scenarios where the Universe is reheated to temperatures <math><mrow><mo>≲</mo><mn>100</mn><mtext> </mtext><mi>GeV</mi></mrow></math> by the decay of long-lived massive particles into energetic SM particles. Before its thermalization, the center-of-mass energy in collisions between such a particle and a particle from the ambient plasma can be higher than the typical sphaleron mass, even if the temperature of the plasma itself is much lower. Optimistic estimates for the high energy enhancement of the sphaleron cross section suggest that successful baryogenesis is possible for reheating temperatures as low as 0.1–1 GeV. With a simple extension of the SM, sufficient baryon production should be achieved by enhancing the W-boson coupling even if more pessimistic results for the sphaleron rate are correct. In both cases, if the two to many sphaleron reaction is significant enough for the baryogenesis, the same process can be probed in collider and cosmic-ray experiments. Complementing such experimental tests, a significantly improved understanding of the two to many sphaleron rate in the nonperturbative coupling regime is mandatory to determine whether this scenario is viable. Finally, we briefly discuss the possible origin of the required <math><mi>C</mi><mi>P</mi></math> violation.

Japan

Wen Yin

High energy sphalerons for baryogenesis at low temperatures