<p>The origin of neutrino masses remains unknown to date. One popular idea involves interactions between neutrinos and ultralight dark matter, described as fields or particles with masses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>ϕ</mi></msub><mo>≪</mo><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi></math>. Due to the large phase-space number density, this type of dark matter exists in coherent states and can be effectively described by an oscillating classical field. As a result, neutrino mass-squared differences undergo field-induced interference in spacetime, potentially generating detectable effects in oscillation experiments. We demonstrate that if <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><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>, the mechanism becomes sensitive to dark matter density fluctuations, which suppresses the oscillatory behavior of flavor-changing probabilities as a function of neutrino propagation distance in a model-independent way, thereby ruling out this regime. Furthermore, by analyzing data from the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), a benchmark long-baseline reactor experiment, we show that the hypothesis of a dark origin for the neutrino masses is disfavored for <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><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>, compared to the case of constant mass values in vacuum. This result holds at more than the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>4</mn><mi>σ</mi></mrow></math> level across different datasets and parameter choices. The mass range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><mo>≲</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math> can be further tested in current and future oscillation experiments by searching for time variations (rather than periodicity) in oscillation parameters.</p>

China

Andrew Cheek

Italy

Luca Visinelli

Hong-Yi Zhang

Testing the Dark Origin of Neutrino Masses with Oscillation Experiments

The <math><msub><mi>S</mi><mn>8</mn></msub><mo>/</mo><msub><mi>σ</mi><mn>8</mn></msub></math> tension in the large-scale structure can be explained by decaying dark matter with an almost degenerate spectrum and small enough decay width. Here we propose the Gemini dark matter model, which contains a heavy mother particle <math><msub><mi>χ</mi><mn>3</mn></msub></math> and two twins <math><msub><mi>χ</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></math>, which are almost degenerate in mass and are produced at the same time. The dark sector is charged under the same Froggatt-Nielsen symmetry that can explain the hierarchy of the Standard Model Yukawa couplings. The slightly heavier <math><msub><mi>χ</mi><mn>2</mn></msub></math> decays into <math><msub><mi>χ</mi><mn>1</mn></msub></math> and the axionic component of the flavon, which washes out the small-scale structure and resolves <math><msub><mi>S</mi><mn>8</mn></msub><mo>/</mo><msub><mi>σ</mi><mn>8</mn></msub></math> tension. We present the production mechanism of Gemini dark matter and viable parameter regions. We find that, despite the preferred dark matter mass being <math><mrow><mi>O</mi><mo>(</mo><mn>1</mn><mo>)</mo><mi>–</mi><mi>O</mi><mo>(</mo><mn>100</mn><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>keV</mi></mrow></math>, they constitute cold dark matter. The Gemini dark matter model predicts an abundance of dark radiation that will be probed in future measurements of the cosmic microwave background.

Yu-Cheng Qiu

Liang Tan

Gemini dark matter

The Hawking evaporation of primordial black holes (PBH) reheats the Universe locally, forming hot spots that survive throughout their lifetime. We propose to use the temperature profile of such hot spots to calculate the decay rate of metastable vacua in cosmology, avoiding inconsistencies inherent to the Hartle-Hawking or Unruh vacuum. We apply our formalism to the case of the electroweak vacuum stability and find that a PBH energy fraction <math><mi>β</mi><mo>&gt;</mo><mn>7</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>80</mn></mrow></msup><msup><mrow><mo>(</mo><mi>M</mi><mo>/</mo><mi>g</mi><mo>)</mo></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msup></math> is ruled out for black holes with masses <math><mn>0.8</mn><mspace width="0.2em"></mspace><mi>g</mi><mo>&lt;</mo><mi>M</mi><mo>&lt;</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>15</mn></mrow></msup><mspace width="0.2em"></mspace><mi>g</mi></math>.

United Kingdom

Louis Hamaide

Lucien Heurtier

Shi-Qian Hu

Poland

Primordial black holes are true vacuum nurseries

There is no known reason that dark matter interactions with the Standard Model should couple to neutrons and protons in the same way. This isospin violation can have large consequences, modifying the sensitivity of existing and future direct detection experimental constraints by orders of magnitude. Previous works in the literature have focused on the zero-momentum limit which has its limitations when extending the analysis to the Non-Relativistic Effective Field Theory basis (NREFT). In this paper, we study isospin violation in a detailed manner, paying specific attention to the experimental setups of liquid noble detectors. We analyse two effective Standard Model gauge invariant models as interesting case studies as well as the more model-independent NREFT operators. This work demonstrates the high degree of complementarity between the target nuclei xenon and argon. Most notably, we show that the Standard Model gauge-invariant formulation of the standard spin-dependent interaction often generates a sizeable response from argon, a target nuclei with zero spin. This work is meant as an update and a useful reference to model builders and experimentalists.

Darren Price

Ellen Sandford

Isospin-violating dark matter at liquid noble detectors: new constraints, future projections, and an exploration of target complementarity

In this article, we study the potential of direct detection experiments to explore the parameter space of general non-standard neutrino interactions (NSI) via solar neutrino scattering. Due to their sensitivity to neutrino-electron and neutrino-nucleus scattering, direct detection provides a complementary view of the NSI landscape to that of spallation sources and neutrino oscillation experiments. In particular, the large admixture of tau neutrinos in the solar flux makes direct detection experiments well-suited to probe the full flavour space of NSI. To study this, we develop a re-parametrisation of the NSI framework that explicitly includes a variable electron contribution and allows for a clear visualisation of the complementarity of the different experimental sources. Using this new parametrisation, we explore how previous bounds from spallation source and neutrino oscillation experiments are impacted. For the first time, we compute limits on NSI from the first results of the XENONnT and LUX-ZEPLIN experiments, and we obtain projections for future xenon-based experiments. These computations have been performed with our newly developed software package, SNuDD. Our results demonstrate the importance of using a more general NSI parametrisation and indicate that next generation direct detection experiments will become powerful probes of neutrino NSI.

United States

Dorian Amaral

Spain

David Cerdeño

Patrick Foldenauer

A direct detection view of the neutrino NSI landscape

Many cosmological phenomena lead to the production of primordial black holes in the early Universe. These phenomena often create a population of black holes with extended mass and spin distributions. As these black holes evaporate via Hawking radiation, they can modify various cosmological observables, lead to the production of dark matter, modify the number of effective relativistic degrees of freedom, <math><msub><mi>N</mi><mi>eff</mi></msub></math>, source a stochastic gravitational wave background and alter the dynamics of baryogenesis. We consider the Hawking evaporation of primordial black holes that feature nontrivial mass and spin distributions in the early Universe. We demonstrate that the shape of such a distribution can strongly affect most of the aforementioned cosmological observables. We outline the numerical machinery we use to undertake this task. We also release a new version of FRISBHEE that handles the evaporation of primordial black holes with an arbitrary mass and spin distribution throughout cosmic history.

Yuber F. Perez-Gonzalez

Jessica Turner

Evaporation of primordial black holes in the early Universe: Mass and spin distributions

The Froggatt-Nielsen (FN) mechanism provides an attractive way of generating the determined fermion mass hierarchy and quark mixing matrix elements in the Standard Model (SM). Here we extend it by coupling the FN field, the flavon, to a dark sector containing one or more dark matter particles which are produced non-thermally sequentially through flavon production. Non-thermal flavon production occurs efficiently via freeze-in and through field oscillations. We explore this in the regime of high-scale breaking Λ of the global U(1)FN group and at the reheating temperature T  R  ≪ Λ where the flavon remains out of equilibrium at all times. We identify phenomenologically acceptable regions of T  R  and the flavon mass where the relic abundance of dark matter and other cosmological constraints are satisfied. In the case of one-component dark matter we find an effective upper limit on the FN charges at high Λ, i.e.   <math> <msubsup> <mi>Q</mi> <mi>FN</mi> <mi>DM</mi> </msubsup> <mo>≤</mo> <mn>13</mn> </math>  $$ {Q}_{\textrm{FN}}^{\textrm{DM}}\le 13 $$ . In the multi-component dark sector scenario the dark matter can be the heaviest dark particle that can be effectively stable at cosmological timescales, alternatively it can be produced sequentially by decays of the heavier ones. For scenarios where dark decays occur at intermediate timescales, i.e. t ~ 0.1 − 1028 s, we find that existing searches can effectively probe interesting regions of parameter space. These searches include indirect probes on decays such as γ-ray and neutrino telescopes as well as analyses of the Cosmic Microwave Background, as well as constraints on small scale structure formation from the Lyman-α forest. We comment on the future prospects of such probes, place projected sensitivities, and discuss how this scenario could accommodate the cosmological S 8 tension.

Jacek Osiński

Leszek Roszkowski

Sebastian Trojanowski

Dark matter production through a non-thermal flavon portal

We study how the evaporation of primordial black holes (PBHs) can affect the production of dark matter (DM) particles through thermal processes. We consider fermionic DM interacting with Standard Model particles via a spin-1 mediator in the context of a freeze-out or freeze-in mechanism. We show that when PBHs evaporate after dominating the Universe’s energy density, PBHs act as a source of DM and continuously inject entropy into the visible sector that can affect the thermal production in three qualitatively different ways. We compute the annihilation cross sections which account for the interactions between and within the PBH produced and thermally produced DM populations, and establish a set of Boltzmann equations which we solve to obtain the correct relic abundance in those different regimes and confront the results with a set of different cosmological constraints. We provide analytic formulas to calculate the relic abundance for the freeze-out and freeze-in mechanism in a PBH dominated early Universe. We identify regions of the parameter space where the PBHs dilute the relic density and thermalization occurs. Furthermore, we have made our code that numerically solves the Boltzmann equations publicly available.

Belgium

Puerto Rico

Primordial black hole evaporation and dark matter production. II. Interplay with the freeze-in or freeze-out mechanism

Hawking evaporation of black holes in the early Universe is expected to copiously produce all kinds of particles, regardless of their charges under the Standard Model gauge group. For this reason, any fundamental particle, known or otherwise, could be produced during the black hole lifetime. This certainly includes dark matter (DM) particles. This paper improves upon previous calculations of DM production from primordial black holes (PBH) by consistently including the greybody factors, and by meticulously tracking a system of coupled Boltzmann equations. We show that the initial PBH densities required to produce the observed relic abundance depend strongly on the DM spin, varying in about <math><mo>∼</mo><mn>2</mn></math> orders of magnitude between a spin-2 and a scalar DM in the case of nonrotating PBHs. For Kerr PBHs, we have found that the expected enhancement in the production of bosons reduces the initial fraction needed to explain the measurements. We further consider indirect production of DM by assuming the existence of additional and unstable degrees of freedom emitted by the evaporation, which later decay into the DM. For a minimal setup where there is only one heavy particle, we find that the final relic abundance can be increased by at most a factor of <math><mo>∼</mo><mn>4</mn></math> for a scalar heavy state and a Schwarzschild PBH, or by a factor of <math><mo>∼</mo><mn>4.3</mn></math> for a spin-2 particle in the case of a Kerr PBH.

Primordial black hole evaporation and dark matter production. I. Solely Hawking radiation

We consider the treatment of fermionic dark matter interacting with photons via dimension-5 and -6 effective operators, arguing that one should always use hypercharge gauge field form factors, instead of those of the photon. Beyond the simple observation that the electromagnetic form factor description breaks down at the electroweak scale, we show how the additional couplings to the Z boson predicted by the hypercharge form factors modify the relic density calculation and indirect detection limits for dark matter masses of a few tens of GeV and above. Furthermore, constraints from the invisible Z decay width can be competitive for masses below 10 GeV. We review the phenomenology of hypercharge form factors at the LHC as well as for direct and indirect detection experiments. We highlight where the electromagnetic and hypercharge descriptions lead to wildly different conclusions about the viable parameter space and the relative sensitivity of various probes, namely vector boson fusion versus mono-jet constraints from the LHC, and indirect versus direct searches, for larger dark matter masses. We find that the dimension-5 operators are strongly constrained by direct detection bounds, while for dimension-6 operators LHC mono-jet searches are competitive or better than the other probes we consider.