arXiv subjects

Xuan-Lin Su

Publications and source records attributed to Xuan-Lin Su.

5 recordsLinked to original sources

arXiv2026

Fermion Condensate Inflation, Dynamical Waterfall Mechanism and Primordial Black Holes

Fermion condensate inflation, where inflation emerges from four-fermion interactions induced by spacetime torsion, removes the need for additional scalar fields beyond the Standard Model. In this framework, the fermion field can be decomposed into two distinguished sectors, each giving rise to bound states. After integrating out fermions, the bound fields play the roles of the inflaton and the auxiliary fields, resembling hybrid inflation with a waterfall mechanism. The inclusion of an axial chemical potential naturally introduces a mechanism to end inflation and trigger instant preheating. During the waterfall phase, the effective potential of the fermion condensate supports the formation of non-topological solitons such as Q-balls, which act as seeds of primordial black holes. This model is intrinsically connected to Chern-Simons gravity, which implies a parity-violating universe. Consequently, both the primordial black hole (PBH) dark-matter abundance and parity-violation signatures could provide observational tests of the model.

hep-th↗

arXiv2025

Hybrid Inflation from Fermion Condensate

We investigate how inflation can emerge from four-fermion interactions generated by spacetime torsion, eliminating the need for additional scalar fields beyond the Standard Model. We partition fermions in two sectors and introduce two bound fields. In the effective theory approach, once all the fermions have been integrated out, the bound fields serve as the inflaton and the auxiliary field, in analogy to the hybrid inflation and accounting for a waterfall (hybrid) mechanism. The inclusion of an axial chemical potential naturally facilitates the end of reheating. During the waterfall regime, the effective potential governing the fermion condensate supports the formation of non-topological solitons, known as Q-balls, which can be accounted for seeding primordial black holes (PBHs).

gr-qc↗

arXiv2025

Emergent Gravity from Topological Quantum Field Theory: Stochastic Gradient Flow Perspective away from the Quantum Gravity Problem

We propose a scenario according to which the ultraviolet completion of General Relativity is realized through a stochastic gradient flow towards a topological BF theory. Specifically, we consider the stochastic gradient flow of a pre-geometric theory proposed by Wilczek. Its infrared limit exists, and corresponds to a fixed point where stochastic fluctuations vanish. Diffeomorphism symmetries are restored in this limit, where the theory is classical and expressed by the Einstein-Hilbert action. The infrared phase then corresponds to the classical theory of General Relativity, the quantization of which becomes meaningless. Away from the infrared limit, in the pre-geometric phase of the stochastic gradient flow, the relevant fields of the Wilczek theory undergo stochastic fluctuations. The theory can be quantized perturbatively, generating corrections to the classical Einstein-Hilbert action. The stochastic gradient flow also possesses an ultraviolet fixed point. The theory flows to a topological BF action, to which non-perturbative quantization methods can be applied. Two phase transitions occur along the thermal time dynamics, being marked by: i) the breakdown of the topological BF symmetries in the ultraviolet regime, which originates the pre-geometric phase described by the Wilczek theory; ii) the breakdown of the parental symmetries characterizing the Wilczek theory, from which General Relativity emerges. The problem of quantizing the Einstein-Hilbert action of gravity finally becomes redundant.

gr-qc↗

arXiv2023

Scrambling Power of Soft Photons

Observable scattering processes entail emission-absorption of soft photons. As these degrees of freedom go undetected, some information is lost. Whether some of this information can be recovered in the observation of the hard photons, depends of the actual pattern of the scrambling of information. We compute the information scrambling of photon scattering by the tripartite mutual information in terms of the 2-Renyi entropy, and find a finite amount of scrambling is present. The developed procedure thus sheds novel light on the black hole information loss paradox, showing that scrambling is a byproduct of decoherence achieved by the scattering system in its interaction with the environment, due to the emission-absorption of soft photons in fully unitary processes.

hep-th↗

arXiv2023

The scrambling power of gravity in black hole radiation

The black hole information paradox remains a profound challenge in theoretical physics. Among the proposed resolutions, the soft-hair approach stands out for its independence from any specific quantum gravity model. In this paper, we investigate how the inclusion of soft degrees of freedom in the unitary evolution of quantum electrodynamics, within a spacetime collapsing into a Reissner-Nordstrom black hole, leads to information scrambling. By evaluating the tripartite mutual information of this unitary evolution, we estimate the degree of information scrambling in the corresponding quantum channel. Our results show that the presence of soft degrees of freedom induces scrambling of information initially encoded in hard degrees of freedom, driven by quantum electrodynamics interactions and the nontrivial transformations arising from the non-uniqueness of the vacuum in the collapsing spacetime. This lays the groundwork for a deeper understanding of the black hole information paradox, particularly the mechanisms behind information scrambling.

gr-qc↗