<p>In this work, we show that ultralight dark photons, which couple to the Standard Model photon through kinetic mixing, can potentially source galactic scale magnetic fields. Although these magnetic fields would be too weak to detect at present in galaxies due to plasma screening effects, we show that dark photons can provide the seed magnetic field strength (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>20</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">G</mi></math>) required for dynamo amplification in galaxies. Such dynamo-amplified magnetic fields are consistent with observations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">μ</mi><mi mathvariant="normal">G</mi></math> strength galactic magnetic fields.</p>

United States

Joshua Berger

Amit Bhoonah

Canada

Joseph Bramante

J. Leo Kim

China

Ningqiang Song

Lawrence M. Widrow

Galactic magnetic fields seeded by ultralight dark photons

<p>We demonstrate a new technique to search for dark compact objects. When dark matter comprising a dark compact object interacts with photons, the compact object can disperse light traveling though it. As these objects pass between Earth and a distant star, they act as “lampshades” that dim the star. We examine how dimming effects from clumps of dark matter in the Galaxy could be searched for in microlensing surveys, which measure the brightness of stars as a function of time. Using the EROS-2 and OGLE surveys, we show that a dimming analysis of existing data can be used to constrain dark sectors and could be used to discover dark matter in compact objects.</p>

Melissa D. Diamond

Dimming Starlight with Dark Compact Objects

We demonstrate that nongravitational interactions between dark matter and baryonic matter can affect structural properties of galaxies. Detailed galaxy simulations and analytic estimates demonstrate that dark matter which collects inside white dwarf stars and ignites type Ia supernovae can substantially alter star formation, stellar feedback, and the halo density profile through a dark matter induced baryonic feedback process, distinct from usual supernova feedback in galaxies.

Javier F. Acevedo

Haipeng An

Yilda Boukhtouchen

Mark L. A. Richardson

Lucy Sansom

Dark matter induced baryonic feedback in galaxies

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.

India

Nirmal Raj

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

We demonstrate a novel mechanism for producing dark compact objects and black holes through a dark sector, where all the dark matter can be dissipative. Heavy dark sector particles with masses above <math><msup><mn>10</mn><mn>4</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> can come to dominate the Universe and yield an early matter-dominated era before big bang nucleosynthesis (BBN). Density perturbations in this epoch can grow and collapse into tiny dark matter halos, which cool via self-interactions. The typical halo size is set by the Hubble length once perturbations begin growing, offering a straightforward prediction of the halo size and evolution depending on one’s choice of dark matter model. Once these primordial halos have formed, a thermal phase transition can then shift the Universe back into radiation domination and standard cosmology. These halos can continue to collapse after BBN, resulting in the late-time formation of fragmented dark compact objects and sub-solar-mass primordial black holes. We find that these compact objects can constitute a sizable fraction of all of dark matter. The resulting fragments can have masses between <math><msup><mn>10</mn><mn>20</mn></msup></math> and <math><msup><mn>10</mn><mn>32</mn></msup><mtext> </mtext><mtext> </mtext><mi>g</mi></math>, with radii ranging from <math><msup><mn>10</mn><mrow><mo>−</mo><mn>2</mn></mrow></msup></math> to <math><msup><mn>10</mn><mn>5</mn></msup><mtext> </mtext><mtext> </mtext><mi>m</mi></math>, while the black holes can have masses between <math><msup><mn>10</mn><mn>8</mn></msup></math> and <math><msup><mn>10</mn><mn>34</mn></msup><mtext> </mtext><mtext> </mtext><mi>g</mi></math>. Furthermore, a unique feature of this model is the late-time formation of black holes which can evaporate today. We compare where these objects lie with respect to current primordial black hole and massive (astrophysical) compact halo object constraints.

Christopher V. Cappiello

Melissa Diamond

Qinrui Liu

Aaron C. Vincent

Dissipative dark cosmology: From early matter dominance to delayed compact objects

A new approach is presented to compute entropy for massless scalar quantum fields. By perturbing a skewed correlation matrix composed of field operator correlation functions, the mutual information is obtained for disjoint spherical regions of size r at separation R, including an expansion to all orders in r/R. This approach also permits a perturbative expansion for the thermal field entropy difference in the small temperature limit (T ≪ 1/r).

Andrew Buchanan

Perturbative method for mutual information and thermal entropy of scalar quantum fields

Dark matter is typically assumed not to couple to the photon at tree level. While annihilation to photons through quark loops is often considered in indirect detection searches, such loop-level effects are usually neglected in direct detection, as they are typically subdominant to tree-level dark-matter–nucleus scattering. However, when dark matter is lighter than around 100 MeV, it carries so little momentum that it is difficult to detect with nuclear recoils at all. We show that loops of low-energy hadronic states can generate an effective dark-matter–photon coupling, and thus lead to scattering with electrons even in the absence of tree-level dark-matter–electron scattering. For light mediators, this leads to an effective fractional electric charge that may be very strongly constrained by astrophysical observations. Current and upcoming searches for dark-matter–electron scattering can thus set limits on dark-matter–proton interactions down to 1 MeV and below.

Limiting Light Dark Matter with Luminous Hadronic Loops

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

United Kingdom

Light dark matter accumulating in planets: Nuclear scattering

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.

Spain

Bradley J. Kavanagh

Scattering Searches for Dark Matter in Subhalos: Neutron Stars, Cosmic Rays, and Old Rocks

Large composite dark matter states source a scalar binding field that, when coupled to Standard Model nucleons, provides a potential under which nuclei recoil and accelerate to energies capable of ionization, radiation, and thermonuclear reactions. We show that these dynamics are detectable for nucleon couplings as small as <math><msub><mi>g</mi><mi>n</mi></msub><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>17</mn></mrow></msup></math> at dark matter experiments, where the greatest sensitivity is attained by considering the Migdal effect. We also explore type-Ia supernovae and planetary heating as possible means to discover this type of dark matter.