arXiv subjects

Varun Kushwaha

Publications and source records attributed to Varun Kushwaha.

3 recordsLinked to original sources

arXiv2026

Primordial spectra from modified Bekenstein-Hawking entropy law

Many approaches to quantum gravity predict logarithmic corrections to the Bekenstein-Hawking entropy. Within the spacetime-thermodynamic description of gravity, such corrections lead to modified gravitational field equations. We study their effect on primordial perturbations during standard single-field slow-roll inflation. We derive the evolution equation for the comoving curvature perturbation and show that it retains the standard Mukhanov--Sasaki form, with the quantum-gravity correction entering through the time-dependent effective frequency. We compute the scalar and tensor primordial spectra at next-to-next-to-next-to-leading order ($\mathrm{N}^3\mathrm{LO}$) in the Hubble-flow parameters, keeping the leading contribution from the logarithmic correction. The scalar spectrum remains nearly scale invariant, but the quantum-gravity correction shifts its tilt and runnings. Free tensor modes still propagate as in general relativity, although on the quantum-gravity-corrected background. This different response of the two sectors shifts both the tensor-to-scalar ratio and the single-field consistency relation, which provide the starting point for tracing the model's signatures through the post-inflationary evolution and into the CMB.

gr-qc↗

arXiv2026

Causality from the spectrum: Emergence of causal order from process-matrix mereology

In Hamiltonian systems, the only basis-independent quantity is the spectrum. Given a spectrum, quantum mereology seeks preferred tensor-product decompositions into local subsystems, leading to the emergence of locality. Causal order, however, remains fixed by the Hamiltonian time evolution. In contrast, higher-order quantum theory permits more general processes that need not possess a definite global causal order. In the process-matrix framework, specifying a process requires a choice of subsystems corresponding to the input and output Hilbert spaces of each agent. A change of basis redefines both the agents and the corresponding decompositions into subsystems, while leaving the spectrum of the process matrix invariant. Here, we study how causality arises from this spectrum. First, we derive spectral constraints on processes compatible with definite causal order. Second, we show that, in the thermodynamic limit, generic quantum processes admit a preferred decomposition with a definite causal order. This suggests a mechanism for the emergence of classical causality only from algebraic ingredients.

quant-ph↗

arXiv2026

Area Scaling of Dynamical Degrees of Freedom in Regularised Scalar Field Theory

How many canonical degrees of freedom does a quantum field theory actually use during its Hamiltonian evolution? For a UV/IR-regularised classical scalar field, we address this question directly at the level of phase-space dynamics by identifying the minimal symplectic dimension required to reproduce a single trajectory by an autonomous Hamiltonian system. Using symplectic model order reduction as a structure-preserving diagnostic, we show that for the free scalar field this minimal dimension is controlled not by the volume-extensive number of discretised field variables, but by the much smaller number of distinct normal-mode frequencies below the ultraviolet cutoff. In flat space, this leads to an area-type scaling with the size of the region, up to slowly varying corrections. On geodesic balls in maximally symmetric curved spaces, positive curvature induces mild super-area growth, while negative curvature suppresses the scaling, with the flat result recovered smoothly in the small-curvature limit. Numerical experiments further indicate that this behaviour persists in weakly interacting $\lambda\phi^4$ theory over quasi-integrable time scales. Beyond counting, the reduced dynamics exhibits a distinctive internal structure: it decomposes into independent oscillator blocks, while linear combinations of these blocks generate a larger family of apparent field modes whose Poisson brackets are governed by a projector rather than the identity. This reveals a purely classical and dynamical mechanism by which overlapping degrees of freedom arise, without modifying canonical structures by hand. Our results provide a controlled field-theoretic setting in which area-type scaling and overlap phenomena can be studied prior to quantisation, helping to identify which aspects of such structures--often discussed in holographic contexts--can already arise from classical Hamiltonian dynamics.

hep-th↗