arXiv subjects

Bekir Baytaş

Publications and source records attributed to Bekir Baytaş.

10 recordsLinked to original sources

arXiv2026

Semiclassical multi-mode squeezed states in harmonic cosmology

Harmonic cosmology is an algebraic framework based on the $\mathfrak{su}(1,1)$ Lie algebra that underlies the effective dynamics of loop quantum cosmology and group field theory. Focusing on the multimode bosonic realization of $\mathfrak{su}(1,1)$, we construct multimode squeezed states in harmonic cosmology and analyze their semiclassical properties by computing the relative uncertainties of the volume operator at the kinematical level. In contrast to single-mode squeezed vacua, which invariably exhibit large quantum fluctuations, we find that the relative uncertainty of the volume can be made arbitrarily small when the number of modes is large, even without displacement. Our results demonstrate that a kinematical squeezed vacuum state with a large number of independent modes can behave semiclassically providing insights into the quantum nature of bouncing cosmologies and the emergence of a classical universe.

gr-qc↗

arXiv2026

Degenerate Limits of Scalar-Tensor Gravity

We study the degenerate limits of the scalar-tensor theory of gravity in its Hamiltonian connection dynamics formulation. The degenerate limit of the spatial triad is effectuated by a local scaling transformation of the triad, which leads to the degenerate limits of all other geometric quantities and relations in the connection dynamics. We derive the constraints for the degenerate scalar-tensor theory of gravity and discuss their physical implications.

gr-qc↗

arXiv2026

Bosonic and fermionic statistics in nonperturbative quantum gravity

The relation between spin and statistics in quantum field theory relies on Poincaré invariance, a symmetry that is lost in the presence of a gravitational field, and replaced in general relativity by the principle of general covariance. In a nonperturbative approach to quantum gravity, beyond the picture of gravitational perturbations propagating on a flat background, it is an open question whether the gravitational field must still satisfy a bosonic statistics. By implementing the principle of general covariance through the requirement of invariance under active diffeomorphisms in loop quantum gravity, we find that the space of kinematical states of the gravitational field includes not only bosonic states, but also subspaces of fermionic and mixed statistics.

gr-qc↗

arXiv2025

A class of entangled and diffeomorphism-invariant states in loop quantum gravity: Bell-network states

Bell-network states constitute a class of diffeomorphism-invariant and entangled states of the geometry within loop quantum gravity (LQG) that satisfy an area-law for the entanglement entropy in the limit of large spins. The fluctuations of the geometry for a Bell-network state are entangled, similar to those in the semiclassical limit as described by quantum field theory in curved spacetimes. We present a comprehensive analysis of the effective geometry of Bell-network states on a dipole graph. This analysis provides a detailed characterization of the quantum geometry of a class of diffeomorphism-invariant, area-law states representing homogeneous and isotropic configurations in loop quantum gravity, which may be explored as boundary states for the dynamics of the theory.

gr-qc↗

arXiv2024

Effective geometry of Bell-network states on a dipole graph

Bell-network states are a class of entangled states of the geometry that satisfy an area-law for the entanglement entropy in a limit of large spins and are automorphism-invariant, for arbitrary graphs. We present a comprehensive analysis of the effective geometry of Bell-network states on a dipole graph. Our main goal is to provide a detailed characterization of the quantum geometry of a class of diffeomorphism-invariant, area-law states representing homogeneous and isotropic configurations in loop quantum gravity, which may be explored as boundary states for the dynamics of the theory. We found that the average geometry at each node in the dipole graph does not match that of a flat tetrahedron. Instead, the expected values of the geometric observables satisfy relations that are characteristic of spherical tetrahedra. The mean geometry is accompanied by fluctuations with considerable relative dispersion for the dihedral angle, and perfectly correlated for the two nodes.

gr-qc↗

arXiv2024

Category-theoretic formulation of relational materialism

This brief brochure is intended to present a philosophical theory known as relational materialism. We introduce the postulates and principles of the theory, articulating its ontological and epistemological content using the language of category theory. The identification of any existing entity is primarily characterized by its relational, finite, and non-static nature. Furthermore, we provide a categorical construction of particularities within the relational materialist onto-epistemology. Our objective is to address and transform a specific perspective prevalent in scientific communities into a productive network of philosophical commitments.

physics.hist-ph↗

arXiv2018

Gluing polyhedra with entanglement in loop quantum gravity

In a spin-network basis state, nodes of the graph describe un-entangled quantum regions of space, quantum polyhedra. In this paper we show how entanglement between intertwiner degrees of freedom enforces gluing conditions for neighboring quantum polyhedra. In particular we introduce Bell-network states, entangled states defined via squeezed vacuum techniques. We study correlations of quantum polyhedra in a dipole, a pentagram and a generic graph. We find that vector geometries, structures with neighboring polyhedra having adjacent faces glued back-to-back, arise from Bell-network states. We also discuss the relation to Regge geometries. The results presented show clearly the role that entanglement plays in the gluing of neighboring quantum regions of space.

gr-qc↗

arXiv2017

Minisuperspace models of discrete systems

A discrete quantum spin system is presented in which several modern methods of canonical quantum gravity can be tested with promising results. In particular, features of interacting dynamics are analyzed with an emphasis on homogeneous configurations and the dynamical building-up and stability of long-range correlations. Different types of homogeneous minisuperspace models are introduced for the system, including one based on condensate states, and shown to capture different aspects of the discrete system. They are evaluated with effective methods and by means of continuum limits, showing good agreement with operator calculations whenever the latter are available. As a possibly quite general result, it is concluded that an analysis of the building-up of long-range correlations in discrete systems requires non-perturbative solutions of the dynamical equations. Some questions related to stability can be analyzed perturbatively, but suggest that matter couplings may be relevant for this question in the context of quantum cosmology.

gr-qc↗

arXiv2016

On the space of non-Gaussian fields with single-clock bispectra

We develop a mathematical construction of non-Gaussian fields whose bispectra satisfy the single-clock inflation consistency relation. At the same order that our basis for bispectra recovers the two simplest single clock templates, we also find a third orthogonal template which has the single clock squeezed limit, peaks in folded configurations, and has very small coupling in the equilateral limit. We explore the map between templates and operators in a very general Lagrangian for single-clock fluctuations and find no significant overlap between the new template and models in the literature. We comment on the physical implications of this conclusion. Our findings add support for the idea that both theory and data driven considerations will be best served if next generation non-Gaussianity constraints are made in a basis that uses the degree of coupling between long and short wavelength modes as an organizing principle.

astro-ph.CO↗

arXiv2015

Non-local bispectra from super cosmic variance

We present examples of non-Gaussian statistics that can induce bispectra matching local and non-local (including equilateral) templates in biased sub-volumes. We find cases where the biasing from coupling to long wavelength modes affects only the power spectrum, only the bispectrum or both. Our results suggest that ruling out multi-field scenarios is quite difficult: some measurements of the scalar correlations, including the shape of the bispectrum, can be consistent with single-clock predictions even when cosmic variance from super-horizon modes is at work. Furthermore, if observations of the density perturbations rule out single-clock inflation, we will face a serious cosmic variance obstacle in drawing any further conclusions about the particle physics origin of the scalar fluctuations.

astro-ph.CO↗