Primordial Black Hole production in Critical Higgs Inflation (1705.04861v3)

Abstract: Primordial Black Holes (PBH) arise naturally from high peaks in the curvature power spectrum of near-inflection-point single-field inflation, and could constitute today the dominant component of the dark matter in the universe. In this letter we explore the possibility that a broad spectrum of PBH is formed in models of Critical Higgs Inflation (CHI), where the near-inflection point is related to the critical value of the RGE running of both the Higgs self-coupling $\lambda(\mu)$ and its non-minimal coupling to gravity $\xi(\mu)$. We show that, for a wide range of model parameters, a half-domed-shaped peak in the matter spectrum arises at sufficiently small scales that it passes all the constraints from large scale structure observations. The predicted cosmic microwave background spectrum at large scales is in agreement with Planck 2015 data, and has a relatively large tensor-to-scalar ratio that may soon be detected by B-mode polarization experiments. Moreover, the wide peak in the power spectrum gives an approximately lognormal PBH distribution in the range of masses $0.01 - 100\,M_\odot$, which could explain the LIGO merger events, while passing all present PBH observational constraints. The stochastic background of gravitational waves coming from the unresolved black-hole-binary mergers could also be detected by LISA or PTA. Furthermore, the parameters of the CHI model are consistent, within $2\sigma$, with the measured Higgs parameters at the LHC and their running. Future measurements of the PBH mass spectrum could allow us to obtain complementary information about the Higgs couplings at energies well above the EW scale, and thus constrain new physics beyond the Standard Model.

• The paper demonstrates that Critical Higgs Inflation produces a half-domed curvature spectrum that leads to an approximately lognormal distribution of primordial black hole masses.
• The paper shows that the Higgs boson, with a non-minimal coupling to gravity, can act as the inflaton while satisfying CMB and large-scale structure constraints.
• The paper highlights the potential of primordial black holes as dark matter candidates and suggests observational tests via gravitational wave signals to probe high-energy physics.

Primordial Black Hole Production in Critical Higgs Inflation

The paper "Primordial Black Hole production in Critical Higgs Inflation" investigates the emergence of Primordial Black Holes (PBHs) from single-field inflation models, specifically within the framework of Critical Higgs Inflation (CHI). The potential role of PBHs as a significant component of dark matter is a central theme, driven by the recent detection of gravitational waves from binary black hole mergers.

The research examines the possibility that the Higgs boson, with a non-minimal coupling to gravity, acts as the inflaton field. This choice is motivated by the established physics of the Higgs and the need for a minimal set of new theoretical assumptions beyond the Standard Model (SM). The CHI model leverages the running of the Higgs self-coupling and the non-minimal gravitational coupling through renormalization group equations (RGE).

Key findings highlight the emergence of a half-domed-shaped peak in the curvature power spectrum of the inflationary perturbations. This peak is constrained by current large-scale structure observations and is consistent with the cosmic microwave background (CMB) data from Planck 2015, including a tensor-to-scalar ratio conducive to future detection by B-mode polarization experiments. The broad peak also enables an approximately lognormal distribution of PBH masses (ranging from 0.01 to 100 $M_\odot$), which is compatible with the masses involved in observed LIGO merger events.

The research contends that the CHI framework not only aligns with SM Higgs parameters within observed experimental constraints but also offers a predictive avenue for higher-energy physics. Importantly, this paper aligns the inflaton's physics with the next-generation thrusts in primordial cosmology and particle physics.

In terms of implications, the work opens a pathway for CHI to interface with gravitational wave astronomy and further explores PBH as a viable candidate for dark matter. The potential detection of gravitational waves from massive BH binaries and stochastic backgrounds offers observational tests for this model. Moreover, the model presents an opportunity to constrain new physics at scales above the electroweak level, potentially reconciling the stability and fine-tuning puzzles of the Higgs potential.

This paper suggests significant theoretical and observational avenues for future paper. Particularly, the precise measurement of PBH mass spectra and gravitational wave backgrounds will not only refine the CHI predictions but also provide robust tests for the model's viability, thereby contributing to a deeper understanding of both the early universe and the nature of dark matter. As research progresses, further integration of particle physics experiments and cosmological observations will be crucial to validate the theoretical predictions outlined in this paper.