Dark, Cold, and Noisy: Constraining Secluded Hidden Sectors with Gravitational Waves (1811.11175v2)

Abstract: We explore gravitational wave signals arising from first-order phase transitions occurring in a secluded hidden sector, allowing for the possibility that the hidden sector may have a different temperature than the Standard Model sector. We present the sensitivity to such scenarios for both current and future gravitational wave detectors in a model-independent fashion. Since secluded hidden sectors are of particular interest for dark matter models at the MeV scale or below, we pay special attention to the reach of pulsar timing arrays. Cosmological constraints on light degrees of freedom restrict the number of sub-MeV particles in a hidden sector, as well as the hidden sector temperature. Nevertheless, we find that observable first-order phase transitions can occur. To illustrate our results, we consider two minimal benchmark models: a model with two gauge singlet scalars and a model with a spontaneously broken $U(1)$ gauge symmetry in the hidden sector.

• The paper demonstrates that gravitational wave signals from first-order phase transitions in secluded hidden sectors can serve as a novel probe for dark matter.
• It develops a model-independent sensitivity analysis, highlighting how detectors like PTAs, LISA, DECIGO, and the Einstein Telescope can capture low-temperature transitions.
• By examining benchmark models with distinct thermal histories and N_eff constraints, the study defines viable parameter spaces for future gravitational wave observations.

Analysis of Gravitational Wave Signals from Hidden Sector Phase Transitions

The paper presented in the paper "Dark, Cold, and Noisy: Constraining Secluded Hidden Sectors with Gravitational Waves" investigates the potential of gravitational wave (GW) detection to explore the properties of secluded hidden sectors, focusing largely on those related to dark matter. The research explores how first-order phase transitions within these sectors—occurring at temperatures dissimilar to our Standard Model (SM) sector—could produce GW signals detectable by current and forthcoming observatories.

Gravitational Waves from Phase Transitions

Gravitational waves in this context are stochastic backgrounds originating from cosmological first-order phase transitions. The paper considers how such transitions in hidden sectors—composed of sub-MeV particles—could imprint themselves on the GW background. Such sectors are conjectured to influence the very early universe, potentially even preceding Big Bang Nucleosynthesis (BBN). The authors provide a comprehensive paper of GW signals by developing model-independent sensitivity analysis for different configurations of GW detectors, including both ground-based and space-borne observatories.

Key Contributions and Methodology

1. Analyzing Light Hidden Sectors:

The authors critically examine sub-MeV hidden sectors, noting the cosmological constraints imposed by the effective number of neutrino species $N_{\text{eff}}$. Such constraints limit the number of sub-MeV particles and the hidden sector temperature. Pulsar Timing Arrays (PTAs) are highlighted as particularly promising for detecting phase transitions occurring at very low temperatures.

2. Temperature Differences:

The paper explores scenarios where hidden and SM sectors have different thermal histories. This divergence in temperatures is crucial since any observable gravitational signal must manifest despite keeping $N_{\text{eff}}$ within acceptable bounds.

3. Benchmark Models:

Two minimal models are scrutinized: one involving two gauge singlet scalars and another employing a spontaneously broken $U(1)$ gauge symmetry. By examining these models, the paper illustrates viable parameter spaces for phase transitions that are potentially detectable within the constraining framework of $N_{\text{eff}}$.

Numerical Analysis and Results

The paper offers a rigorous numerical analysis that establishes the parameter spaces in which current and future observational facilities might detect GW signals indicative of such hidden sector transitions. The analysis reveals that PTAs, along with ground and space-based GW detectors like LISA, DECIGO, and the Einstein Telescope, possess the capability to probe energy scales where such sectoral transitions could feasibly occur. Especially relevant are transitions at very low temperatures ($T_h \approx \text{keV}$), where hidden sectors must remain cooler than the visible SM sector (${h} < 1$) to avoid cosmology-based constraints.

Implications and Prospects for AI

This research extends theoretical and practical implications alike. Practically, the constraints and sensitivities identified establish a ground for experimental teams focusing on GW detection to consider secluded hidden sectors as plausible sources of observable signals. Theoretically, this work underscores the complexity within the field of particle physics and cosmology regarding the detection of new physics via gravitational waves.

Regarding future prospects in Artificial Intelligence, there is significant potential for AI applications to refine signal-extraction techniques from complex datasets obtained by GW observatories, enhancing our capacity to discern subtle signals indicative of hidden phase transitions.

In conclusion, the paper meticulously outlines a pathway using gravitational wave astronomy to provide insights into hidden sector dynamics. The rigorous analytical framework, combined with careful consideration of observational capabilities, positions this work as a pivotal contribution to our understanding of dark matter-linked physics and the early universe.