Supernova 1987A Constraints on Sub-GeV Dark Sectors, Millicharged Particles, the QCD Axion, and an Axion-like Particle (1803.00993v2)

Abstract: We consider the constraints from Supernova 1987A on particles with small couplings to the Standard Model. We discuss a model with a fermion coupled to a dark photon, with various mass relations in the dark sector; millicharged particles; dark-sector fermions with inelastic transitions; the hadronic QCD axion; and an axion-like particle that couples to Standard Model fermions with couplings proportional to their mass. In the fermion cases, we develop a new diagnostic for assessing when such a particle is trapped at large mixing angles. Our bounds for a fermion coupled to a dark photon constrain small couplings and masses <200 MeV, and do not decouple for low fermion masses. They exclude parameter space that is otherwise unconstrained by existing accelerator-based and direct-detection searches. In addition, our bounds are complementary to proposed laboratory searches for sub-GeV dark matter, and do not constrain several "thermal" benchmark-model targets. For a millicharged particle, we exclude charges between 10^-9 to a few times 10^-6 in units of the electron charge; this excludes parameter space to higher millicharges and masses than previous bounds. For the QCD axion and an axion-like particle, we apply several updated nuclear physics calculations and include the energy dependence of the optical depth to accurately account for energy loss at large couplings. We rule out a hadronic axion of mass between 0.1 and a few hundred eV, or equivalently bound the PQ scale between a few times 10^4 and 10^8 GeV, closing the hadronic axion window. For an axion-like particle, our bounds disfavor decay constants between a few times 10^5 GeV up to a few times 10^8 GeV. In all cases, our bounds differ from previous work by more than an order of magnitude across the entire parameter space. We also provide estimated systematic errors due to the uncertainties of the progenitor.

• The paper establishes stringent constraints on sub-GeV dark sector models and millicharged particles through detailed analysis of SN1987A data.
• It employs kinetic mixing and inelastic dark matter scenarios, significantly narrowing unexplored parameter space in particle models.
• Enhanced limits on the QCD axion and axion-like particles are achieved by incorporating higher-order chiral perturbation theory and plasma interaction effects.

Constraints on Sub-GeV Dark Sectors and Axions from Supernova 1987A

The paper "Supernova 1987A Constraints on Sub-GeV Dark Sectors, Millicharged Particles, the QCD Axion, and an Axion-like Particle" by Chang, Essig, and McDermott, presents a comprehensive analysis of how the observation of Supernova 1987A (SN1987A) imposes constraints on various models of dark matter (DM) and axion physics. Essentially, the paper explores the limits this historic astronomical event places on new, weakly interacting light particles that may couple to the Standard Model (SM) fields, especially those below the GeV scale.

Dark Sector Models and Constraints

The authors present an analysis of how SN1987A impacts constraints on several dark sector models. The paper considers models wherein DM fermions are coupled to a dark photon through kinetic mixing with the SM photon. The paper distinguishes between different hierarchical mass relations, such as whether the dark photon is heavier or lighter than twice the DM mass, examining both elastic and inelastic DM scenarios.

For dark matter coupled to a kinetically mixed dark photon, the paper derives bounds for heavy dark matter (where the dark photon cannot decay to DM) and light dark matter (where such decay is prompt). The derived constraints close a significant portion of otherwise unexplored parameter space for sub-GeV DM models.

Notably, the paper also explores models of inelastic DM, where a small mass splitting exists between two DM states, introducing a unique interplay between production and decay processes in the supernova environment. Constraints are significantly stronger when inelastic processes dominate due to suppressed dark matter trapping.

Millicharged particles, characterized by a small electric charge, are also explored. The paper updates constraints on these from previous works, prominently by considering refined models of plasma interactions in stellar environments.

Axions and Axion-like Particles

The analysis extends to axion physics, particularly focusing on the Quantum Chromodynamics (QCD) axion, which arises from the Peccei-Quinn solution to the strong CP problem. The work provides updated constraints, noting that previous analyses have utilized several approximations that may underestimate the true bounds on axion parameters. By incorporating higher-order calculations from chiral perturbation theory, this paper suggests significantly enhanced constraints on both the axion mass and the Peccei-Quinn scale.

Furthermore, axion-like particles (ALPs) with extended parameter spaces are considered. The constraints from SN1987A help delineate the viable parameter space for ALPs, particularly those with Yukawa-like couplings, bridging gaps left by laboratory-based searches.

Implications and Future Directions

The constraints derived from SN1987A have significant implications for ongoing and future searches for sub-GeV dark matter and axions. The work illustrates that stellar observations, particularly supernovae, provide a unique, complementary probe to laboratory searches. Importantly, several benchmark models remain viable and are testable in upcoming experiments, emphasizing a comprehensive approach whereby astrophysical and laboratory data collectively inform the search for new physics.

Future developments may focus on refining these constraints with improved supernova models and a more nuanced understanding of particle interactions in stellar interiors. Advances in both simulations of core-collapse supernovae and experiments aimed at directly detecting sub-GeV DM will be crucial. This paper highlights the potential of combining experimental, observational, and theoretical approaches to deepen our understanding of particle physics beyond the Standard Model.