Current and most upcoming neutrino detectors can only reach a dark matter annihilation cross section to neutrinos larger than the standard freeze-out value, but they open intriguing detection avenues for nonstandard dark matter paradigms. An important corollary of these nonstandard scenarios is relic dark matter annihilation after neutrino decoupling, which was previously overlooked in constraining MeV-scale dark matter. However, by combining the contributions from entropy injection during neutrino decoupling and from nonthermal neutrino energy release after decoupling, we derive significant constraints on the annihilation cross section to neutrinos, which in some mass regimes become stronger than the current bounds. Furthermore, we find that the lower bounds on dark matter masses become inconclusive under the recent data releases from the Dark Energy Spectroscopic Instrument, South Pole Telescope 3G, and Atacama Cosmology Telescope collaborations. These bounds determine the extent to which upcoming neutrino detectors will probe dark matter annihilation into neutrinos.

Japan

Shinya Kanemura

Shao-Ping Li

Dibyendu Nanda

Bounds and detection of MeV-scale dark matter annihilation to neutrinos

The radiative seesaw model with gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mrow><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub><mo>×</mo><msub><mi mathvariant="double-struck">Z</mi><mn>2</mn></msub></math> extension is a well-motivated scenario that gives consistent predictions of active neutrino masses and the abundance of dark matter. Majorana masses of right-handed neutrinos, the lightest of which can be identified as dark matter, are given by the spontaneous breaking of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mrow><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> gauge symmetry. We revisit this model with the latest constraints from dark-matter searches, neutrino oscillations, flavor experiments, and collider experiments. We examine several benchmark scenarios and identify the valid parameter space of this model, finding that there are still allowed regions under the latest experimental constraints. We present new viable benchmark scenarios for this model, i.e., the right-handed neutrino dark-matter scenario and the scalar dark-matter scenario. We also mention the testability of these benchmark scenarios in future experiments.

Yushi Mura

Guohao Ying

Revisiting the model for radiative neutrino masses with dark matter in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mstyle mathvariant="normal"><mi>U</mi></mstyle><mo stretchy="false">(</mo><mn>1</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></mrow></math> gauge theory

The origin of neutrino masses can be simply attributed to a new scalar beyond the Standard Model. We demonstrate that leptogenesis can explain the baryon asymmetry of the universe already in such a minimal framework. Different from traditional leptogenesis, the realization here exploits the thermal behavior of leptons at finite temperatures, which is otherwise kinematically forbidden in vacuum. We present detailed calculations of the CP asymmetry in the Schwinger-Keldysh Closed-Time-Path formalism, and compute the asymmetry evolution via the Kadanoff-Baym equation. Such minimal forbidden neutrinogenesis establishes a direct link between the baryon asymmetry and the CP-violating phase from neutrino mixing, making the scenario a compelling target in neutrino oscillation experiments. Complementary probes from cosmology, flavor physics and colliders are also briefly discussed.

Forbidden neutrinogenesis

We study two Higgs doublet models with successful electroweak baryogenesis but without cancellations of electric dipole moments (EDMs). For the baryogenesis, additional scalar bosons are favored to couple mainly with the top quark with CP violations. However, if they also couple to light fermions of the Standard Model, the model is limited severely by EDMs, and additional CP phases irrelevant to the baryogenesis are often introduced to cancel the contributions to the EDMs. Alternatively, we consider a scenario where the light-fermion couplings are suppressed to avoid the constraints. In our scenario, it is found that the leading contributions arise in the top-quark EDMs at the two-loop level. They induce the electron, neutron, and proton EDMs via radiative corrections. Since there is no additional CP-violating phase, they are correlated with the baryon asymmetry. We show that our scenario is compatible with the current experimental bounds and is within the scope of future EDM experiments.

Masashi Aiko

Motoi Endo

Electroweak baryogenesis in 2HDM without EDM cancellation

The electric dipole moment is examined in a three-loop neutrino mass model with dark matter originally proposed in Aoki et al. [$\textit{Phys. Rev. Lett.}$ (2009) 051805]. The model contains a $\textit{CP}$-violating phase in the Higgs potential which plays an important role in electroweak baryogenesis and is thus expected to explain the baryon asymmetry of the Universe simultaneously. However, such a $\textit{CP}$-violating phase is severely constrained by the measurements of the electron electric dipole moment (eEDM), and a suppression mechanism for the eEDM is necessary to explain the observed baryon asymmetry while avoiding the constraint. In this paper, we examine neutrino mass, lepton-flavor-violating processes, dark matter, and the eEDM in the model. We show that the eEDM can be suppressed by destructive interference between the $\textit{CP}$-violating phases in the Higgs sector and the dark sector with large $\textit{CP}$-violating phases. We propose some benchmark scenarios including $\textit{O}$(1) $\textit{CP}$-violating phases where tiny neutrino mass and dark matter can be explained while avoiding all current experimental and theoretical constraints. These $\textit{CP}$-violating phases are expected to be large enough to generate the observed baryon asymmetry in the electroweak baryogenesis scenario.

South Korea

Kazuki Enomoto

Sora Taniguchi

The electric dipole moment in a model for neutrino mass, dark matter and baryon asymmetry of the Universe

To explain the baryon asymmetry in the early universe via leptogenesis, quantum corrections to new particles are commonly invoked to generate the necessary <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> asymmetry. We demonstrate, however, that a large <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> asymmetry can already arise from standard model leptons. The mechanism relies on resummation of soft leptons at finite temperatures. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> asymmetry, which is kinematically forbidden in vacuum, can be resonantly enhanced from thermally resummed leptons by seven orders of magnitude. Contrary to the resonance from exotic particles, we show that the resonant enhancement from soft leptons is protected by controlled widths under finite-temperature perturbation theory. We quantify such <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> asymmetries in leptogenesis with secluded flavor effects and comment on the significance and application. The mechanism exploits the maximal role of leptons themselves, featuring low-scale leptogenesis, minimal model buildings, and dark matter cogenesis.

Resonant Forbidden <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="italic">CP</mi></mrow></math> Asymmetry from Soft Leptons

Leading two-loop contributions to the di-photon decay of the Higgs boson are evaluated for the first time in the inert doublet model (IDM). We employ for this calculation the Higgs low-energy theorem, meaning that we obtain corrections to the Higgs decay process by taking Higgs-field derivatives of the leading two-loop contributions to the photon self-energy. Specifically, we have included corrections involving inert BSM Higgs bosons and gauge bosons, as well as external-leg contributions involving inert scalars, gauge bosons and fermions. Our calculation has been performed with a full on-shell renormalization, and in the gauge-less limit. Moreover, we performed two independent calculations, using the background-field method and the pinch technique, in order to apply the Higgs low-energy theorem consistently, and found full agreement between the two calculations. We investigate our results numerically in two scenarios of the IDM: one with a light dark matter (DM) candidate (Higgs resonance scenario), and another with all additional scalars heavy (heavy Higgs scenario). In both cases, we find that the inclusion of two-loop corrections qualitatively modifies the behavior of the decay width, compared with the one-loop (i.e. leading) order, and that they increase the deviation from the Standard Model. Furthermore, we demonstrate that the inclusion of the newly-computed two-loop corrections is essential to reliably interpret the observation or non-observation of a deviation in the Higgs di-photon decay width at current and future colliders.

Germany

Johannes Braathen

Leading two-loop corrections to the Higgs di-photon decay in the inert doublet model

We suggest a simplified model that simultaneously addresses the dark matter problem and gives rise to top-quark flavor changing neutral current (FCNC) interactions at the one-loop order. The model consists of two extra <math><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><msub><mo>)</mo><mi>L</mi></msub></math> gauge singlets: a colored mediator of spin zero (<math><mi>S</mi></math>) and a right-handed fermion (<math><mi>χ</mi></math>); both are odd under an ad hoc <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry. The right-handed fermion plays the role of the dark matter candidate. In this model, the presence of the two dark sector particles generates one-loop induced FCNC decays of the top quark into light quarks and bosons such as the gluon, the photon, the <math><mi>Z</mi></math> boson, or the Higgs boson. As a case study, we analyze the top-quark FCNC decays into light quarks (<math><mi>u</mi></math> or <math><mi>c</mi></math>) and <math><mi>Z</mi></math> or Higgs bosons. We then study the reliable solutions to the dark matter problem by estimating the regions in the parameter space that are consistent with the Planck measurement of the dark matter relic density. We also revisit the bounds from the searches of dark matter in events with at least one high-<math><msub><mi>p</mi><mi>T</mi></msub></math> jet and large missing transverse energy at the Large Hadron Collider (LHC). We then define four benchmark points that are consistent with the existing constraints from collider experiments and cosmology. We finally estimate, for these benchmark scenarios, the rates of a broad range of channels that can be used to probe the connection between the top FCNC transitions and dark matter, both at the HL-LHC and at a future 100 TeV collider.

Adil Jueid

Dark matter as the trigger of flavor changing neutral current decays of the top quark

In order to realize an electroweak first-order phase transition, a category of extended Higgs models with relatively large self-coupling constants is often considered. In such a scenario, the running coupling constants can blow up at an energy scale much below the Planck scale. To clarify the allowed parameter space of the model, it is important to evaluate the scale where perturbative calculation breaks down. In the renormalization group equation analysis using the mass-independent renormalization scheme, we need a matching condition to connect the low energy theory and the high energy theory. Consequently, the analysis depends on the details of the matching condition. On the other hand, an analysis with the mass-dependent beta function can be performed in a simpler way because the threshold effect is automatically included in the beta function. In this paper, using the mass-dependent beta function, we discuss the application limit of perturbative calculations at the one-loop level. First, we explain the essence of our method and compare our results with those based on the mass-independent beta function in a toy model with two complex scalar fields. We then apply our method to a more realistic model, i.e., the inert doublet model. We find that, in our method, in which the threshold effect is automatically included, the energy scale where the perturbative calculation breaks down can be higher than the one using the mass-independent beta function, especially when the blowup scale is relatively low.

Criterion of perturbativity with the mass-dependent beta function in extended Higgs models

Understanding symmetry of extended Higgs models helps to construct the theory beyond the standard model and gives important insights for testing these models by experiments. The custodial symmetry plays an important role as a leading principle to construct non-minimal Higgs sectors. On the other hand, new sources of CP violation in the Higgs sector are essentially important to explain the baryon asymmetry of the Universe. In the two Higgs doublet model, it has been known that the CP violation and the custodial symmetry are not compatible, and thus the CP violating Higgs potential in general violates the custodial symmetry in the Higgs sector. In this paper, we discuss the loop-induced H  ±  W ∓ Z vertices in the two Higgs doublet model, which are induced due to the custodial symmetry violation of the sector of the particles in the loop, and study how the vertices are affected by the CP violation. We calculate the H  ±  W ∓ Z vertices in the most general two Higgs doublet model with the CP violation at the one-loop level and evaluate the decay modes H  ±  → W  ±  Z caused by these vertices. We obtain new contributions to the H  ±  W ∓ Z vertices from the CP violating part of the model, in addition to the known contributions from the CP conserving part. Moreover, we find that an asymmetry between the decays H + → W + Z and H  −  → W  −  Z is caused by the CP violating phases in the model, some of which are important for the electroweak baryogenesis. We also briefly mention testability of these vertices at future collider experiments.