Decay of a scalar condensate via interactions with (quasi-)particles is of interest to many fields in physics, including cosmology. In cosmology, the decay of an inflaton condensate leads to the production of daughter particles and reheating of the Universe. In computing the decay rate, two quantum field theoretic approaches can be found in the literature: one is based on parametric resonance of mode functions of the daughter particle; another is based on the $\textit{S}$-matrix of a coherent state and Feynman-diagrammatic perturbation theory. We modify the latter from the previous literature in a way that manifests what we are computing and does not include unwanted Feynman diagrams. We notice the equivalence of these two approaches and demonstrate it by explicitly computing the decay rate at lower orders in the double expansion of the amplitude of coherent oscillation (or narrow resonance) and velocity of the daughter particle.

Poland

Ayuki Kamada

Japan

Kodai Sakurai

Decay of a scalar condensate in two different approaches

Q-ball dark matter is one of the candidates for the macroscopic dark matter: Q-ball is a non-topological solitonic configuration, whose stability can be ensured by global charge and energy conservation. One of the crucial factors for discovering signatures from the Q-ball dark matter, is the interactions of the Q-ball dark matter with ordinary matter. In particular, the scattering of ordinary matter off the Q-ball dark matter is important for the direct detection searches, such as paleo-detectors. It was conjectured that quarks incident on the Q-ball were reflected as anti-quarks with a probability of order unity, but it costs the energy of the squark in the Q-ball, which cannot be paid in the scattering of ordinary matter off the Q-ball dark matter. In addition, once a proton is reflected as an anti-proton, the Q-ball obtains the electromagnetic charge. In this study, we revisit the scattering process of quarks with the Q-ball with taking into account the energy cost of the scattering and the electromagnetic charge-up of the Q-ball.

China

Takumi Kuwahara

Keiichi Watanabe

Revisiting Q-ball interactions with matters

<p>Composite asymmetric dark matter (ADM) is the framework that naturally explains the coincidence of the baryon density and the dark matter density of the Universe. Through a portal interaction sharing particle-antiparticle asymmetries in the Standard Model and dark sectors, dark matter particles, which are dark-sector counterparts of baryons, can decay into antineutrinos and dark-sector counterparts of mesons (dark mesons) or dark photon. Subsequent cascade decay of the dark mesons and the dark photon can also provide electromagnetic fluxes at late times of the Universe. The cosmic-ray constraints on the decaying dark matter with the mass of 1–10 GeV has not been well studied. We perform comprehensive studies on the decay of the composite ADM by combining the astrophysical constraints from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>±</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math> ray. The constraints from cosmic-ray positron measurements by AMS-02 are the most stringent at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>≳</mo><mn>2</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>: a lifetime should be larger than the order of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mn>26</mn></msup><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">s</mi></math>, corresponding to the cutoff scale of the portal interaction of about <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mn>8</mn></msup><mi>–</mi><msup><mn>10</mn><mn>9</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. We also perform the dedicated analysis for the neutrino monoenergetic signals at Super-Kamiokande and Hyper-Kamiokande due to the atmospheric neutrino background in the energy range of our interest.</p>

Saikat Das

Kohta Murase

Deheng Song

Composite asymmetric dark matter with a dark photon portal: Multimessenger tests

The decay of the mediator particle into standard model (SM) particles plays a significant role in exploring the dark sector scenario. We consider such a decay, taking the dark photon mediator as an example that mixes with the SM photon. We find that it requires a careful analysis of the decay rate in the presence of an SM vector boson (e.g., $\textit{Z}$ boson, $\textit{ρ}$ meson, and true muonium, etc.) nearly degenerate with the mediator particle in mass. The decay rate of the mediator particle calculated in the mass eigenstate basis agree with the correct result, given by the imaginary parts of the poles for the vector boson propagators, when the mixing parameter is smaller than a specific value. In such a case, the decay rate calculated by treating the mixing as a perturbative parameter is in agreement with the correct result. We clarify specific values for the mixing parameter quantitatively using several concrete examples of the SM vector bosons degenerate with the dark photon. When the mass mixing between the vector boson and dark photon is smaller (larger) than the decay width of the vector boson, the latter (former) method to calculate the decay rate of the mediator particle gives the correct result.

Shigeki Matsumoto

Yu Watanabe

Yuki Watanabe

Mediator decay through mixing with degenerate spectrum

Dark matter self-scattering is one of key ingredients for small-scale structure of the Universe, while dark matter annihilation is important for the indirect measurements. There is a strong correlation between the velocity-dependent self-scattering cross section and the Sommerfeld enhancement factor for the dark matter annihilation cross section. In this study, we formulate a direct relation between them by the use of Watson’s (initial state/final state) theorem and Omnès solution, and our formulation reproduces the Sommerfeld enhancement factor, which directly computed by solving the Schrödinger equation, from the scattering phase shift.

Ami Patel

Quantum theory of dark matter scattering

Dark pion is a promising candidate for the strongly interacting massive particle dark matter. A large pion self-coupling m  π /f  π  tends to be required for correct relic abundance, and hence the partial-wave amplitudes can violate the perturbative unitarity even for the coupling within naïve perturbative regime. We improve the partial-wave amplitudes in order to satisfy the optical theorem. We demonstrate that the improvement is relevant only for semi-relativistic pions, and thus this does not affect the self-scattering cross section at the cosmic structures. We also discuss the impact of the improvement of the πππ → ππ scattering process, and we find that there is an upper bound on m  π  at which the correct relic abundance is never achieved even at large m  π /f  π  due to the optical theorem.

Shin Kobayashi

Perturbative unitarity of strongly interacting massive particle models

The LHC lifetime frontier will probe dark sector in near future, and the visible decay searches at fixed-target experiments have been exploring dark sector. Composite asymmetric dark matter with dark photon portal is a promising framework explaining the coincidence problem between dark matter and visible matter. Dark strong dynamics provides rich structure in the dark sector: the lightest dark nucleon is the dark matter, while strong annihilation into dark pions depletes the symmetric components of the dark matter. Dark photons alleviate cosmological problems. Meanwhile, dark photons make dark hadrons long-lived in terrestrial experiments. Moreover, the dark hadrons are produced through the very same dark photon. In this study, we discuss the visible decay searches for composite asymmetric dark matter models. For a few GeV dark nucleons, the LHC lifetime frontier, MATHUSLA and FASER, has a potential to discover their decay when kinetic mixing angle of dark photon is ϵ ≳ 10 −4. On the other hand, fixed-target experiments, in particular SeaQuest, will have a great sensitivity to dark pions with a mass below GeV and with kinetic mixing ϵ ≳ 10 −4 in addition to the LHC lifetime frontier. These projected sensitivities to dark hadrons in dark photon parameter space are comparable with the future sensitivities of dark photon searches, such as Belle-II and LHCb.

South Korea

LHC lifetime frontier and visible decay searches in composite asymmetric dark matter models

A nonminimal coupling <math><mi>η</mi></math> has been attracting growing interest particularly in the context of inflation models, though its quantum nature is not clear yet. We study the renormalization of <math><mi>η</mi></math> in the scalar quantum electrodynamics (QED). There are one-loop diagrams, which could give the finite correction to <math><mi>η</mi></math> in the scalar QED. We find that they cancel with each other. We also find no inhomogeneous term of the renormalization group equation (RGE) at the two-loop level, while there could be the two-loop order finite correction. This is similar to other theories, where an inhomogeneous term of the RGE appears only at a higher-loop order: e.g., four-loop order in <math><mi>λ</mi><msup><mi>ϕ</mi><mn>4</mn></msup></math> theory.

Lessons from <math><mrow><msub><mrow><msup><mrow><mi>T</mi></mrow><mrow><mi>μ</mi></mrow></msup></mrow><mrow><mi>μ</mi></mrow></msub></mrow></math> on inflation models: Two-loop renormalization of <math><mi>η</mi></math> in the scalar QED

We study self-interacting dark matter (SIDM) scenarios, where the s-wave self-scattering cross section almost saturates the Unitarity bound. Such self-scattering cross sections are singly parameterized by the dark matter mass, and are featured by strong velocity dependence in a wide range of velocities. They may be indicated by observations of dark matter halos in a wide range of masses, from Milky Way’s dwarf spheroidal galaxies to galaxy clusters. We pin down the model parameters that saturates the Unitarity bound in well-motivated SIDM models: the gauged L  μ  − L  τ  model and composite asymmetric dark matter model. We discuss implications and predictions of such model parameters for cosmology like the H 0 tension and dark-matter direct-detection experiments, and particle phenomenology like the beam-dump experiments.

Hee Kim

Maximally self-interacting dark matter: models and predictions

A strongly interacting massive particle (SIMP) is an interesting candidate for dark matter (DM) because its self-interaction cross section can be naturally strong enough to address the astrophysical problem of small-scale structure formation. A simple model was proposed by assuming a monopole condensation, where composite SIMP comes from a “strongly interacting” <math><mrow><msub><mrow><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mi>d</mi></msub></mrow></math> gauge theory. In the original model, the DM relic abundance is determined by the <math><mn>3</mn><mo>→</mo><mn>2</mn></math> annihilation process via the Wess-Zumino-Witten term. In this paper, we discuss that the DM relic abundance is naturally determined also by a semiannihilation process via a kinetic mixing between the hypercharge gauge boson and the dark <math><mrow><msub><mrow><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mi>d</mi></msub></mrow></math> gauge boson (dark photon). The dark photon can be discovered by LDMX-style missing momentum experiments in the near future.