Cosmological stasis is a phenomenon in which multiple energy components with different equation-of-state parameters maintain constant abundances for an extended period despite the expansion of the universe. In this talk, I review how stasis arises and discuss the possible implications of this phenomenon in observations. These include the enhancement in the growth of matter density...
In causal set theory, spacetime is represented by a locally finite partially ordered set. The abundances of small combinatorial structures can be used to recover information about its continuum geometry. We study how chains and 2-pixies can be used to recover local cosmological quantities in four-dimensional, spatially flat FLRW spacetimes. For causal diamonds centered on a comoving observer,...
How should one define a renormalization scale when spacetime geometry itself is quantum and dynamical? I will discuss a relational formulation of coarse graining in which physical resolution and mode ordering are defined by dynamical geometric observables, while RG flow remains distinct from physical clock evolution.
I will then present a Hamiltonian implementation using the non-perturbative...
Dark matter (DM), a fundamental cosmic component, motivates the study of its influence on black hole (BH) shadows, especially for spinning BHs confirmed by EHT observations. This work generalizes the Schwarzschild BH surrounded by DM to an axisymmetric Kerr BH using the Newman–Janis Algorithm (NJA), investigating the resulting event horizon and ergosphere structures. Employing null geodesics,...
Bootstrapping provides theoretical constraints of the parameter space allowed by the S-matrix properties: analyticity, unitarity, crossing symmetry. It has been applied to constrain different theories without making assumptions about their ultraviolet completions. However, its application in the forward limit of the scattering amplitudes is problematic when considering graviton exchange.
In...
Non-attractor inflation has drawn significant attention as a class of inflationary models due to its potential to generate primordial black holes (PBHs). However, calculating the one-loop corrections to curvature perturbations in these models has sparked considerable theoretical controversy. We find that symmetry serves as a crucial clue in such loop calculations, and the Ward identity is...
In this talk, I will discuss the focusing of timelike geodesic congruences in $f(Q)$ gravity. I will first introduce geodesic deviation in symmetric teleparallel geometry and the modified Raychaudhuri equation obtained under a Weyl-type nonmetricity ansatz and an additional nonmetricity–acceleration condition. I will then present a focusing condition expressed in terms of the matter...
Entanglement harvesting transfers quantum field correlations to localized probes, yet whether these correlations can alter stable strategic behavior has remained unclear. We formulate a quantum-input game in which two Unruh–DeWitt detectors harvest vacuum entanglement from a free massless scalar field in $(3+1)$-dimensional Minkowski spacetime. A referee converts this state into payoffs using...
In this work, we address a foundational challenge in quantum field theory on curved spacetime by developing a consistent framework in spherically symmetric loop quantum gravity. We introduce a methodology for defining meaningful superpositions of quantum geometry and matter states near the semiclassical apparent horizon. This is achieved by identifying a restricted subspace of the...
Neutrino self-interactions mediated by a light scalar offer a compelling resolution to cosmological tensions and may naturally arise in neutrino mass generation mechanisms. When the scalar also couples to a light dark-sector fermion, supernova neutrinos can resonantly annihilate with the cosmic neutrino background (C$\nu$B) into invisible dark radiation, depleting the flux en route to Earth....
