We extend the Standard Model (SM) by introducing a U(1)$\textit{′}$ gauge boson and a real pseudo-scalar field, both odd under a ℤ symmetry. The resulting low-energy spectrum consists of a stable vector as the dark matter candidate, and a pseudo-scalar mediator, which interacts with the SM via a Higgs portal coupling and a dimension-five portal connecting it to both the dark and visible photons. We explore the freeze-in of both particles at low reheating temperature, finding a rich yield evolution dynamics in the early Universe. This setup brings a consistent dark matter scenario in which the dark photon relic abundance is generated through freeze-in at low reheating temperatures. In addition to its cosmological viability, the model can be tested at the LHC: Higgs bosons can decay into dark photons and displaced visible photons via the long-lived mediator. These signatures allow us to constrain the Higgs portal coupling using recent searches for non-pointing photons and limits on invisible or undetected Higgs decays. We derive meaningful constraints on the dark matter parameter space, in particular excluding a thermalized mediator in the region compatible with the observed relic abundance.

Chile

Paola Arias

Bastián Díaz Sáez

Uruguay

Lucía Duarte

Peru

Joel Jones-Pérez

Walter Rodriguez

Danilo Zegarra Herrera

Probing displaced (dark)photons from low reheating freeze-in at the LHC

We consider a simple Higgs portal dark matter (DM) model, where the Standard Model is extended with a complex singlet scalar. The imaginary part of the scalar becomes a massive and stable pseudo-Nambu-Goldstone boson, serving as the DM candidate, while the real part gives rise to a second (dark) Higgs boson. We focus on the freeze-in production of the DM, paying particular attention to low-reheating temperature scenarios, where the dark Higgs can be a long-lived particle (LLP). We also explore the phenomenology of this dark Higgs at the LHC and the Future Circular Collider in hadron-hadron mode, discussing its discovery prospects in regions of parameter space consistent with current DM constraints. Our results emphasize the impact of the cosmic reheating dynamics on the DM freeze-in production, and their critical role in interpreting collider signatures. Furthermore, our findings suggest that LLP searches may provide insights into the fundamental dynamics of reheating.

United Arab Emirates

Nicolás Bernal

Giovanna Cottin

Manuel López

Testing frozen-in pNGB dark matter with a long-lived dark Higgs

In this paper, we would like to examine whether the Sáez–Ballester theory admits stable and attractive Bianchi type I inflationary solutions in the presence of a non-minimal coupling between scalar and vector fields such as $$f^2(\phi )F_{\mu \nu }F^{\mu \nu }$$ . As a result, such a solution will be shown to exist within this theory for a suitable setup of fields. Interestingly, the considered Sáez–Ballester theory can be shown to be equivalent to the standard scalar–vector theory via a suitable field redefinition. This means that the obtained solution can be reduced to that derived in an original anisotropic inflation model proposed by Kanno, Soda, and Watanabe. Consequently, the corresponding tensor-to-scalar ratio of this solution turns out to be higher than the latest observational value of the Planck satellite (Planck 2018) due to the fact that $$c_s$$ , the corresponding speed of sound of scalar perturbations of the Sáez–Ballester theory, turns out to be one. This result indicates an important hint that the speed of sound, $$c_s$$ , could play an important role in making the corresponding non-canonical anisotropic inflation cosmologically viable in the light of the Planck 2018 data. To be more specific, we will point out that any modifications of the Sáez–Ballester theory having $$c_s \sim 0.1$$ will have a great potential to be highly consistent with the Planck 2018 data. For heuristic reasons, a simple modified version of the Sáez–Ballester theory will be proposed as a specific demonstration. As a result, we will show that this modified model admits an anisotropic power-law inflationary solution as expected.

Vietnam

Tuan Do

Phung Dong

Duy Nguyen

India

J. Singh

Anisotropic power-law inflation for the Sáez–Ballester theory non-minimally coupled to a vector field

We propose a Majoron-like extension of the Standard Model with an extra global <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>X</mi></mrow></msub></math>-symmetry where neutrino masses are generated through an inverse seesaw mechanism at the 1-loop level. In contrast to the tree-level inverse seesaw, our framework contains dark matter (DM) candidates stabilized by a residual <math><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math>-symmetry surviving spontaneous breaking of the <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>X</mi></mrow></msub></math>-group. We explore the case in which the DM is a Majorana fermion. Furthermore, we provide parameter space regions allowed by current experimental constraints coming from the dark matter relic abundance, (in)direct detection, and charged lepton flavor violation.

Cesar Bonilla

A.E. Cárcamo Hernández

Sergey Kovalenko

Juan Marchant González

Dark matter from a radiative inverse seesaw majoron model

In this research we consider a <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>X</mi></mrow></msub></math> gauge boson acting as a dark matter candidate. The vector dark matter (DM) gets mass when a complex singlet scalar breaks the gauge symmetry spontaneously, adding a second Higgs boson to the spectra. The dark matter candidates communicate with the SM particles via a scalar-Higgs portal. In this work, we concentrate on the masses of the vector dark matter and the scalar mediator below 10 GeV, aka light dark matter. Although we assume thermal freeze-out for the vector DM using the zero-moment of the full Boltzmann equation to calculate the relic abundance, we explore the effects of the second-moment when the vector DM annihilates resonantly. As typically light DM is highly sensitive to CMB bounds, we focus on two thermal mechanisms which alleviate this bound: dark matter annihilation via forbidden channels and near a pole. Other bounds from colliders, thermalization conditions, beam-dump experiments, and astrophysical observations are imposed. Taking into account all the bounds including the direct detection upper limits, the viable space is achieved.

Iran

Amir Amiri

Karim Ghorbani

(sub)GeV dark matter in the (1) Higgs portal model

We explore a simple model containing two singlet scalars as dark matter candidates and a vector-like lepton. Evading collider and dark matter constraints, the model is able to accommodate the correct dark matter relic abundance and the <math><msub><mrow><mo>(</mo><mi>g</mi><mo>−</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>μ</mi></mrow></msub></math> anomaly when the masses of the three new fields are around 100 GeV and the values of the minimum amount of required couplings are order one.

Germany

Singlet scalars as dark matter and the muon ( − 2) Anomaly