The interiors of neutron stars enjoy ideal conditions for the conversion of hadrons to a strange quark phase, theorized to be the stablest form of matter. Though numerous astrophysical means to prompt such a deconfinement phase transition have been suggested, they may be preempted by a large energy barrier for nucleation of quark matter droplets. We will show that interactions of hidden sectors of particles with nucleons may surmount the barrier if it exceeds deca-GeV energies, and spark a phase transition. The neutron star would then, depending on the equation of state of QCD matter, convert to a black hole and/or set off a gamma-ray burst (GRB). Using the observed existence of ancient neutron stars and estimates of the GRB rate, we then set some of the strictest (albeit conditional) limits on dark matter scatters, annihilations, and decays that are tens of orders stronger than those from terrestrial searches. For smaller energy barriers, lower limits on nucleon decay lifetimes of the order of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mn>64</mn></msup><mtext> </mtext><mtext> </mtext><mi>yr</mi></math> may be obtained.

India

Aryaman Bhutani

Nirmal Raj

Zenia Zuraiq

Dark, deep, deconfining: Phase transitions in neutron stars as powerful probes of hidden sectors

The memory burden effect is an explicit resolution to the information paradox by which an evaporating black hole acquires quantum hair, which then suppresses its rate of mass loss with respect to the semiclassical Hawking rate. We show that this has significant implications for particle dark matter that captures in neutron stars and forms black holes that go on to consume the host star. In particular, we show that constraints on the nucleon scattering cross section and mass of spin-0 and spin-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></math> dark matter would be extended by several orders of magnitude.

Ujjwal Basumatary

United States

Anupam Ray

Beyond Hawking evaporation of black holes formed by dark matter in compact stars

In direct searches of dark matter, multiscatter signatures are now being sought to probe scattering cross sections that are large enough to make the detector optically thick to incident particles. We provide some significant updates to the multiscatter program. Using considerations of energy deposition, we derive the reaches in cross section and mass of various proposed large-volume detectors: a kilotonne fiducial mass “module of opportunity” at DUNE, a kilotonne xenon detector suggested for neutrinoless double beta decay, the gaseous detector CYGNUS, and the dark matter detectors XLZD and Argo. Where the velocity vector can be reconstructed event-by-event, the Galactic dark matter velocity distribution may be inferred. We exploit this to show that halo substructure such as tidal streams can be picked up if they make up about 10% of the local dark matter density.

Harsh Aggarwal

Ultraheavy multiscattering dark matter: DUNE, CYGNUS, other kilotonne detectors, and tidal streams

We identify the maximum cross sections probed by single-scatter weakly interacting massive particle (WIMP) searches in dark matter direct detection. Owing to Poisson fluctuations in scatter multiplicity, these ceilings scale logarithmically with mass for heavy dark matter and often lie in regions probed by multiscatter searches. Using a generalized formula for single-scatter event rates we recast WIMP searches by the quintal-to-tonne scale detectors XENON1T, XENONnT, LZ, PANDAX-II, PANDAX-4T, DarkSide-50, and DEAP-3600 to obtain ceilings and floors up to a few <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> mass and <math><msup><mn>10</mn><mrow><mo>−</mo><mn>22</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></math> per nucleus cross section. We do this for coherent, geometric, isospin-violating xenophobic and argophobic spin-independent scattering, and neutron-only and proton-only spin-dependent scattering. Future large-exposure detectors would register an almost irreducible background of atmospheric neutrinos that would determine a dark matter sensitivity ceiling that we call the “neutrino roof,” in analogy with the well-studied “neutrino floor.” Accounting for this background, we estimate the reaches of the 10–100 tonne scale DarkSide-20k, DARWIN/XLZD, PANDAX-xT, and Argo, which would probe many decades of unconstrained parameter space up to the Planck mass, as well as of <math><msup><mn>10</mn><mn>3</mn></msup><mi>–</mi><msup><mn>10</mn><mn>4</mn></msup><mtext> </mtext><mtext> </mtext><mi>tonne</mi></math> scale noble liquid detectors that have been proposed in synergy with neutrino experiments.

Biprajit Mondal

Neutrino roof: Single-scatter cross section ceilings in dark matter direct detection experiments

We show that dark matter with certain minimal properties can convert the majority of baryons in galaxies to black holes over hundred trillion year timescales. We argue that this has implications for cosmologies which propose that new universes are created in black hole interiors. We focus on the paradigm of cosmological natural selection, which connects black hole production to a universe’s likelihood for existing. Further, we propose that the Universe’s timescale for entropy production could be dynamically linked to black hole production in a naturally selected universe. Our Universe would fit this scenario for models of particle dark matter that convert helium white dwarfs to black holes in around a hundred trillion years, where the dominant source of entropy in our Universe is the helium white dwarfs’ stellar progenitors, which cease forming and burning also in around a hundred trillion years. Much of this dark matter could be discovered at ongoing experiments.

Canada

Joseph Bramante

Cosmology of self-replicating universes in the interior of black holes formed by dark matter-seeded stellar collapse

Cosmologies in which dark matter clumps strongly on small scales are unfavorable to terrestrial detectors that are as yet unexposed to the clumps. I show that subhectometer clumps could trigger thermonuclear runaways by scattering on nuclei in white dwarf cores (carbon and oxygen) and neutron star oceans (carbon), setting off type-Ia-like supernovae and x-ray superbursts, respectively. I consider two scenarios: “dark clusters” that are essentially microhalos and “long-range dark nuggets,” essentially macroscopic composites, with long-range Yukawa baryonic interactions that source the energy for igniting explosions. I constrain dark clusters, weighing between the Planck mass and asteroid masses, and long-range dark nuggets over a wider mass range spanning 40 orders of magnitude. These limits greatly complement searches proposed by myself and co-workers [Phys. Rev. Lett. 128, 231801 (2022)] for scattering interactions of dark clumps in neutron stars, cosmic rays, and prehistoric minerals.

Supernovae and superbursts triggered by dark matter clumps

We present, for the first time, a complete treatment of strongly interacting dark matter capture in planets, taking Earth as an example. We focus on light dark matter and the heating of Earth by dark matter annihilation, addressing a number of crucial dynamical processes which have been overlooked, such as the “ping-pong effect” during dark matter capture. We perform full Monte Carlo simulations and obtain improved bounds on strongly-interacting dark matter from Earth heating and direct detection experiments for both spin-independent and spin-dependent interactions, while also allowing for the interacting species to make up a subcomponent of the cosmological dark matter.

Jason Kumar

Gopolang Mohlabeng

China

United Kingdom

Ningqiang Song

Light dark matter accumulating in planets: Nuclear scattering

We propose new searches for <math><msup><mi>n</mi><mo>′</mo></msup></math>, a dark baryon that can mix with the Standard Model neutron. We show that IsoDAR, a proposal to place an intense cyclotron near a large-volume neutrino detector deep underground, can look for <math><mi>n</mi><mo>→</mo><msup><mi>n</mi><mo>′</mo></msup><mo>→</mo><mi>n</mi></math> transitions with much lower backgrounds than surface experiments. This opportune neutron-shining-through-a-wall search would be possible without any modifications to the primary goals of the experiment and would provide the strongest laboratory constraints on the <math><mi>n</mi><mo>−</mo><msup><mi>n</mi><mo>′</mo></msup></math> mixing for a wide range of mass splitting. We also consider dark neutrons as dark matter and show that their nuclear absorption at deep-underground detectors such as SNO and Borexino places some of the strongest limits in parameter space. Finally, we describe other <math><msup><mi>n</mi><mo>′</mo></msup></math> signatures, such as neutrons shining through walls at spallation sources, reactors, and the disappearance of ultracold neutrons.

Matheus Hostert

David McKeen

Maxim Pospelov

Dark sectors in neutron-shining-through-a-wall and nuclear-absorption signals

Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are generically challenging to uncover at direct detection experiments due to rates suppressed by powers of the local dark matter velocity <math><msub><mi>v</mi><mrow><mi>DM</mi></mrow></msub><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mi>c</mi></math>. However, they may be observed in the dark matter-induced heating of neutron stars, whose steep gravitational potentials prevent such suppression by accelerating infalling particles to semirelativistic speeds. We investigate this phenomenon in the context of two specific, self-consistent scenarios for pseudoscalars coupled to dark matter, and compare the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter. The first “lighter” scenario consists of sub-10 GeV mass dark matter mediated by an axionlike particle, while the second “heavier” scenario has dark matter above 10 GeV mediated by a dark pseudoscalar that mixes with a pseudoscalar from a two-Higgs doublet (the so-called <math><mrow><mn>2</mn><mi>HDM</mi><mo>+</mo><mi>a</mi></mrow></math> model). In both frameworks, we show that imminent measurements of neutron stars will be able to test pseudoscalar-mediated dark matter beyond the reach of direct dark matter searches as well as bounds on the mediators from flavor observables, beam dump experiments, and high-energy colliders.

John Coffey

David E. Morrissey

Neutron star observations of pseudoscalar-mediated dark matter

In many cosmologies dark matter clusters on subkiloparsec scales and forms compact subhalos, in which the majority of Galactic dark matter could reside. Null results in direct detection experiments since their advent four decades ago could then be the result of extremely rare encounters between the Earth and these subhalos. We investigate alternative and promising means to identify subhalo dark matter interacting with standard model particles: (1) subhalo collisions with old neutron stars can transfer kinetic energy and brighten the latter to luminosities within the reach of imminent infrared, optical, and ultraviolet telescopes; we identify new detection strategies involving single-star measurements and Galactic disk surveys, and obtain the first bounds on self-interacting dark matter in subhalos from the coldest known pulsar, PSR J2144–3933; (2) subhalo dark matter scattering with cosmic rays results in detectable effects; (3) historic Earth-subhalo encounters can leave dark matter tracks in Paleolithic minerals deep underground. These searches could discover dark matter subhalos weighing between gigaton and solar masses, with corresponding dark matter cross sections and masses spanning tens of orders of magnitude.