arXiv subjects

I. Y. Park

Publications and source records attributed to I. Y. Park.

At least 19 recordsLinked to original sources

arXiv2026

Influence of finite-temperature effects on CMB power spectrum

We explore the implications of finite-temperature quantum field theory effects on cosmological parameters within the framework of the $Ł$CDM model and its modification. By incorporating temperature-dependent corrections to the cosmological constant, we extend the standard cosmological model to include additional density parameters, $Ω_{Ł_2}$ and $Ω_{Ł_3}$, which arise from finite-T quantum gravitational effects. Using the Cosmic Linear Anisotropy Solving System (CLASS), we analyze the impact of these corrections on the cosmic microwave background power spectrum and compare the results with the Planck 2018 data. Through brute-force parameter scans and advanced machine learning techniques, including quartic regression, we demonstrate that the inclusion of $Ω_{Ł_2}$ and $Ω_{Ł_3}$ improves the model's fit to the {\em fine} structure of the reference power spectrum. Because $Ω_{Ł_2}$ and $Ω_{Ł_3}$ originate from finite-temperature quantum (loop) corrections rather than being introduced as free dark-energy components, they are expected to be small a priori; their smallness is thus a prediction of the framework, not a sign that they are negligible. The improvement of the fit is measured by the coefficient of determination $R^2$ (the fraction of variance in the parameter--distance relation captured by the regression), together with lower mean squared error and lower AIC/BIC scores than those of the $Ł$CDM model. Despite identified methodological limitations, these findings establish an exploratory framework for incorporating finite-temperature quantum corrections into precision cosmology and open new avenues for data-driven exploration of cosmological parameters.

astro-ph.CO↗

arXiv2026

Stochastic analysis of finite-temperature effects on cosmological parameters by artificial neural networks

We explore the impact of finite-temperature quantum gravity effects on cosmological parameters, particularly the cosmological constant $Λ$, by incorporating temperature-dependent quantum corrections into the Hubble parameter. For that purpose, we modify the Cosmic Linear Anisotropy Solving System. We introduce new density parameters, $Ω_{Λ_2}$ and $Ω_{Λ_3}$, arising from finite-temperature quantum gravity contributions, and analyze their influence on the cosmic microwave background power spectrum using advanced machine learning techniques, including artificial neural networks and stochastic optimization. Our results reveal that $Ω_{Λ_2}$ assumes a negative value, consistent with dimensional regularization in renormalization and that the presence of $Ω_{Λ_2}$ as well as $Ω_{Λ_3}$ enhances model accuracy. Numerical analyses demonstrate that the inclusion of these parameters improves the fit to 2018 Planck data. Although further work is required, our results suggest that finite-temperature quantum gravity effects may play a non-negligible role in cosmological evolution. Although the Hubble tension persists, our findings highlight the potential of quantum gravitational corrections in refining cosmological models and motivate further investigation into higher-order thermal effects and polarization data constraints.

astro-ph.CO↗

arXiv2025

Finite-temperature renormalization of Standard Model coupled with gravity, and its implications for cosmology

Finite-temperature one-loop renormalization of the Standard Model, coupled with dynamic metric, is conducted in this study. The entire analysis is coherently carried out by using the refined background field method, applied in the spirit of the Coleman-Weinberg technique. The general form of the propagator, introduced in our previous work to facilitate Feynman diagram computation in a general curved background, proves useful in the presence of time-dependent temperature. Its utilization allows for the renormalization analysis of a FLRW background to essentially reduce to that of a constant finite-T flat spacetime. For infrared physics, the actual curved background should be considered. The implications of our findings for cosmology, particularly the cosmological constant problem and Hubble tension, are discussed.

hep-th↗

arXiv2023

Black hole entropy from non-Dirichlet sectors, and bounce solution

In a series of recent works the relevance of gravitational boundary degrees of freedom and their dynamics in gravity quantization and black hole information has been explored. In this work we further the progress by keenly focusing on the boundary degrees of freedom as the origin of black hole entropy. Wald's entropy formula is scrutinized, and the reason that the Wald's formula correctly captures the entropy of a black hole is examined. Afterwards, limitations of the Wald's method are discussed; a coherent view of entropy based on boundary dynamics is presented. The discrepancy observed in the literature between holographic and Wald's entropies is addressed. We generalize the entropy definition so as to handle a time-dependent black hole. Large gauge symmetry plays a pivotal role. Non-Dirichlet boundary conditions and gravitational analogues of Coleman-De Luccia bounce solutions are central in identifying the microstates and differentiating the origins of entropies associated with different classes of solutions. The result in the present work leads to a view that black hole entropy is entanglement entropy in a thermodynamic setup.

hep-th↗

arXiv2022

Cosmological constant as a finite temperature effect

We reexamine the cosmological constant problem in a finite temperature setup and propose an intriguing possibility of carrying out perturbative analysis by employing a renormalization scheme in which the renormalized Higgs mass (or resummed mass, to be more precise) is taken to be on the order of the CMB temperature. Our proposal hinges on the fact that although the physical value of the cosmological constant does not depend on one's renormalization scheme, whether or not a fine tuning is involved does. The cosmological constant problem is avoided in the sense that the renormalization process no longer requires finetuning. This is achieved essentially by renormalization scheme-independence of a physical quantity, which in turn is assured by bare perturbation theory. The proposal shifts the cosmological constant problem to a peculiarity of the consequent perturbation series for the Higgs mass (and other massive sectors of the Standard Model); the peculiarity is interpreted as an indicator of new physics after the expected mathematical structure of the series is scrutinized. Finite-temperature-induced complexification of the effective potential is observed and its interpretation is given. A consistency check in the cosmology context is suggested.

hep-ph↗

arXiv2021

Quantization of gravity and finite temperature effects

Gravity is perturbatively renormalizable for the physical states which can be conveniently defined via foliation-based quantization. In recent sequels, one-loop analysis was explicitly carried out for Einstein-scalar and Einstein-Maxwell systems. Various germane issues and all-loop renormalizability have been addressed. In the present work we make further progress by carrying out several additional tasks. Firstly, we present an alternative 4D covariant derivation of the physical state condition by examining gauge choice-independence of a scattering amplitude. To this end, a careful dichotomy between the ordinary, and large gauge symmetries is required and appropriate gauge-fixing of the ordinary symmetry must be performed. Secondly, vacuum energy is analyzed in a finite-temperature setup. A variant optimal perturbation theory is implemented to two-loop. The renormalized mass determined by the optimal perturbation theory turns out to be on the order of the temperature, allowing one to avoid the cosmological constant problem. The third task that we take up is examination of the possibility of asymptotic freedom in finite-temperature quantum electrodynamics. In spite of the debates in the literature, the idea remains reasonable.

hep-th↗

arXiv2021

Quantum-gravitational trans-Planckian radiation by a rotating black hole

We recently studied the energy behavior of a quantum-corrected time-dependent black hole. The system analyzed was a quantum-corrected Kerr solution that settles down to a stationary configuration as the time dependence fades out. A trans-Planckian energy scaling in the vicinity of the event horizon resulted, and we proposed the trans-Planckian radiation to be the missing link in the glowing mechanism of active galactic nuclei. The main goal of the present work is to examine the scaling and structure of the radiation by analyzing the quantum momentum density. We again observe a trans-Planckian behavior. Furthermore, the momentum density displays structures that are indicative of a disk-like configuration near the equator and a collimated outflow of matter from the poles. The bipolar outflow (disk-like structure) should be an essential part of the underlying mechanism for jets (accretion disks) of active galactic nuclei.

hep-th↗

arXiv2021

Black hole evolution in quantum-gravitational framework

We found black hole evolution on a quantum-gravitational scattering framework with an aim to tackle the black hole information paradox. With this setup, various pieces of the system information are explicit from the start and unitary evolution is manifest throughout. The scattering amplitudes factorize into the perturbative part and nonperturbative part. The nonperturbative part is dominated by an instanton-type contribution, i.e., a black hole analogue of the Coleman-De Luccia's bounce solution, and we propose that the Hawking radiation be identified with the particles generated by the vacuum decay. Our results indicate that the black hole degrees of freedom are entangled not only with the Hawking modes but also with the pre-Hawking modes. The Wald's entropy charge measures their entanglement. The full quantum-gravitational entropy is defined as the vev of the Wald entropy charge. With this definition a {\em shifted} Page-like curve is generically generated and its quantum extension is readily defined.

hep-th↗

arXiv2020

Revisit of renormalization of Einstein-Maxwell theory at one-loop

In a series of recent works based on foliation-based quantization in which renormalizability has been achieved for the physical sector of the theory, we have shown that the use of the standard graviton propagator interferes, due to the presence of the trace mode, with the 4D covariance. A subtlety in the background field method also requires careful handling. This status of the matter motivated us to revisit an Einstein-scalar system in one of the sequels. Continuing the endeavors, we revisit the one-loop renormalization of an Einstein-Maxwell system in the present work. The systematic renormalization of the cosmological and Newton's constants is carried out by applying the refined background field method. One-loop beta function of the vector coupling constant is explicitly computed and compared with the literature. The longstanding problem of gauge choice-dependence of the effective action is addressed and the manner in which the gauge-choice independence is restored in the present framework is discussed. The formalism also sheds light on background independent analysis. The renormalization involves a metric field redefinition originally introduced by `t Hooft; with the field redefinition the theory should be predictive.

hep-th↗

arXiv2019

Quantum-gravitational trans-Planckian energy of a time-dependent black hole

We continue our recent endeavor in which a time-dependent black hole solution of a one-loop quantum-corrected Einstein-scalar system was obtained and its near-horizon behavior was analyzed. The energy analysis led to a trans-Planckian scaling behavior near the event horizon. In the present work the analysis is extended to a rotating black hole solution of an Einstein-Maxwell-scalar system with a Higgs potential. Although the analysis becomes much more complex compared to that of the previous, we observe the same basic features, including the quantum-gravitational trans-Planckian energy near the horizon.

hep-th↗

arXiv2019

Foliation-based approach to quantum gravity and applications to astrophysics

The recently proposed Holography-inspired approach to quantum gravity is reviewed and expanded. The approach is based on the foliation of the background spacetime and reduction of the offshell states to the physical states. Careful attention is paid to the boundary conditions. It is noted that the outstanding problems such as the cosmological constant problem and black hole information can be tackled from the common thread of the quantized gravity. One-loop renormalization of the coupling constants and the beta function analysis are illustrated. Active galactic nuclei and gravitational waves are discussed as the potential applications of the present quantization scheme to astrophysics.

hep-th↗

arXiv2019

Boundary dynamics in gravitational theories

We present a foliation-focused critical review of the boundary conditions and dynamics of 4D gravitational theories. A general coordinate transformation introduces a new foliation and changes the hypersurface on which a natural boundary condition is imposed; in this sense gauge transformations must be viewed as changing the boundary conditions. The issue of a gauge invariant boundary condition is nontrivial and has been extensively studied in the literature. We turn around the difficulty in obtaining such a boundary condition (and subtleties observed in the main body) and take it as one of the indications of an enlarged Hilbert space so as to include the states satisfying different boundary conditions. Through the systematical reduction procedure we obtain, up to some peculiarities, the explicit form of the reduced Lagrangian that describes the dynamics of the physical states. We examine the new insights offered by the 3D Lagrangian on BMS-type symmetry and black hole information. In particular we confirm that the boundary dynamics is an indispensable part of the system information.

hep-th↗

arXiv2018

Quantization of gravity through hypersurface foliation

We have recently proposed in \cite{Park:2014tia} the quantization of pure 4D Einstein gravity through hypersurface foliation, and observed that the 4D Einstein gravity becomes renormalizable once all (or most) of the unphysical degrees of freedom are removed. In this work, we confirm this observation from a more mathematical angle. In particular, we show that the physical state condition arising from the shift vector constraint connects with the requirement that the manifold admit "totally geodesic (TG) foliation". The TG foliation, in turn, makes it possible to view the 4D manifold as abelian fibration over a 3D base. Associating the abelian fibration with the 4D diffeomorphism leads to reduction of the 4D manifold to 3D, thereby realizing and generalizing the holography of 't Hooft.

gr-qc↗

arXiv2018

Complete Einstein equation from the generalized First Law of Entanglement

Recently it was observed that the first law of Entanglement leads to the linearized Einstein equation. In this paper, we point out that the gravity dual of an relative entropy expression is equivalent to the full non-linear Einstein equation. We also construct an entanglement vector field $V_{E}$ whose flux is the entanglement entropy. The flow of the vector field looks like sewing two space regions along the interface.

hep-th↗

arXiv2018

Quantum-induced trans-Planckian energy near horizon

We study the loop effects on the geometry and boundary conditions of several black hole spacetimes one of which is time-dependent and analyze the energy measured by an infalling observer near their horizons. The finding in the previous works that the loop effects can be drastic is reinforced: they play an important role in the boundary conditions and non-perturbative geometry deformation. One of the channels through which the quantum gravitational effects enter is generation of the cosmological constant. The cosmological constant feeds the time-dependence of a solution. We obtain a trans-Planckian energy in the time-dependent case. The importance of time-dependence for the trans-Planckian energy and black hole information is discussed.

hep-th↗

arXiv2018

One-loop renormalization of a gravity-scalar system

Extending the renormalizability proposal of the physical sector of 4D Einstein gravity, we have recently proposed renormalizability of the 3D physical sector of gravity-matter systems. The main goal of the present work is to conduct systematic one-loop renormalization of a gravity-matter system by applying our foliation-based quantization scheme. In this work we explicitly carry out renormalization of a gravity-scalar system with a Higgs-type potential. With the fluctuation part of the scalar field gauged away, the system becomes renormalizable through a metric field redefinition. We use dimensional regularization throughout. One of the salient aspects of our analysis is how the graviton propagator acquires the"mass" term. One-loop calculations lead to renormalization of the cosmological and Newton's constants. We discuss other implications of our results as well: time-varying vacuum energy density and masses of the elementary particles as well as the potential relevance of Neumann boundary condition for black hole information.

hep-th↗

arXiv2018

4D covariance of holographic quantization of Einstein gravity

It has been observed in [Park 2014] that the physical states of the ADM formulation of 4D Einstein gravity holographically reduce and can be described by a 3D language. Obviously the approach poses the 4D covariance issue; it turns out that there are two covariance issues whose address is the main theme of the present work. Although the unphysical character of the trace piece of the fluctuation metric has been long known, it has not been taken care of in a manner suitable for the Feynman diagram computations; a proper handling of the trace piece through gauge-fixing is the key to more subtler of the covariance issues. As for the second covariance issue, a renormalization program can be carried out covariantly to any loop order at intermediate steps, thereby maintaining the 4D covariance; it is only at the final stage that one should consider the 3D physical external states. With the physical external states, the 1PI effective action reduces to 3D and renormalizability is restored just as in the entirely-3D approach of [Park 2014]. We revisit the one-loop two-point renormalization with careful attention to the trace piece of the fluctuation metric and in particular outline one-loop renormalization of the Newton's constant.

hep-th↗

arXiv2017

Quantum-corrected geometry of horizon vicinity

We study the deformation of the horizon-vicinity geometry caused by quantum gravitational effects. Departure from the semi-classical picture is noted, and the fact that the matter part of the action comes at a higher order in Newton's constant than does the Einstein-Hilbert term is crucial for the departure. The analysis leads to a Firewall-type energy measured by an infalling observer for which quantum generation of the cosmological constant is critical. The analysis seems to suggest that the Firewall should be a part of such deformation and that the information be stored both in the horizon-vicinity and asymptotic boundary region. We also examine the behavior near the cosmological horizon.

hep-th↗