arXiv subjects

J. Polonyi

Publications and source records attributed to J. Polonyi.

At least 19 recordsLinked to original sources

arXiv2025

Classical limit of a scalar quantum field theory

It is well known that a minimal distance emerges in quantum field theories owing to the need to regularize the UV divergences. The macroscopical limit at large minimal distance, weak spatial resolution, is investigated for a self interacting scalar quantum field theory by the help of the renormalization group. The lowering of the cutoff always opens the dynamics hence the renormalization group has to be implemented for open quantum field theories. A strongly coupled non-relativistic scaling regime is found supporting a second order phase transition between weakly and strongly open theories. The weakly (strongly) open bare theories develop into strongly (weakly) open dynamics during the renormalization group flow. The two known conditions of classical limit, the strong decoherence and the suppression of the quantum fluctuations are confirmed for closed bare theories at distances beyond a non-relativistic correlation length.

hep-th↗

arXiv2024

First order phase transition with functional renormalization group method

The renormalization group method, more specifically the Wegner-Houghton equation, is used to find first order phase transitions in a simple scalar field theory with a polynomial potential. An improved definition of the running parameters allows us to explore the renormalization group flow down to the IR end point and to locate phase transitions. Beyond the expected first order transition further radiative correction generated first and second order transitions are found. The phase diagram is reviewed by a Monte-Carlo simulation of the lattice regulated version of the theory but the serious slow down of the convergence prevents us to obtain conclusive results from the simulation.

hep-th↗

arXiv2022

Renormalizing open quantum field theories

The functional renormalization group flow of a scalar field theory with quartic couplings and a sharp spatial momentum cutoff is presented in four-dimensional Minkowski space-time for the bare action by retaining the entanglement of the IR and the UV particle modes. It is argued that the open interaction channels have to be taken into account in quantum field theory defined by the help of a cutoff, and a non-perturbative UV-IR entanglement is found in closed or almost closed models.

hep-th↗

arXiv2020

Renormalization in Minkowski space-time

The multiplicative and the functional renormalization group methods are applied for the four dimensional scalar theory in Minkowski space-time. It is argued that the appropriate choice of the subtraction point is more important in Minkowski than in Euclidean space-time. The parameters of the cutoff theory, defined by a subtraction point in the quasi-particle domain, are complex due to the mass-shell contributions and the renormalization group flow becomes much more involved than its Euclidean counterpart.

hep-th↗

arXiv2018

Euclidean scalar field theory in the bi-local approximation

The blocking step of the renormalization group method is usually carried out by restricting it to fluctuations and to local blocked action. The tree-level, bi-local saddle point contribution to the blocking, defined by the infinitesimal decrease of the sharp cutoff in momentum space, is followed within the three dimensional Euclidean $ϕ^6$ model in this work. The phase structure is changed, new phases and relevant operators are found and certain universality classes are restricted by the bi-local saddle point.

hep-th↗

arXiv2016

Quantum renormalization group

The observed IR and the spectator UV particles of a regulated, cutoff quantum field theory are entangled by their interactions; hence, the IR sector can be described by the help of the density matrix only. The tree-level renormalized trajectory is obtained for a self-interacting scalar field theory, containing the mixed state contributions. One needs a sharp cutoff in the momentum space as regulator to realize the true loss of information, caused by massive particles.

hep-th↗

arXiv2013

Proton scattering on an electron gas

It is shown in the case of proton scattering on an electron gas target that the Closed Time Path formalism can handle final state interactions of the target in equilibrium in a simple and natural manner. The leading order cross section is proportional to the photon density of states. The scattering needs a partial resummation of the perturbation series when the electron gas forms long living quasi-particles with high density of state during the collision. A strong cancellation between real and virtual electron-hole pairs is found in this case.

hep-ph↗

arXiv2012

Exchange of signals around the event horizon in Schwarzschild space-time

Red shift in communication and possibility of interaction is discussed for objects around the event horizon of Schwarzschild space-time. It is pointed out that the arrow of time within the horizon cannot always be inferred by observations carried out outside. Two scenarios are presented for the causal structure of the space-time and it is found that in one of them extended objects fall apart into their elementary constituents by crossing the horizon.

gr-qc↗

arXiv2011

Onset of symmetry breaking by the functional RG method

A numerical algorithm is used to solve the bare and the effective potential for the scalar $ϕ^4$ model in the local potential approximation. An approximate dynamical Maxwell-cut is found which reveals itself in the degeneracy of the action for modes at some scale. This result indicates that the potential develop singular field dependence as far as one can see it by an lgorithm of limited numerical accuracy

hep-th↗

arXiv2010

Quantum censorship in two dimensions

It is pointed out that increasingly attractive interactions, represented by partially concave local potential in the Lagrangian, may lead to the degeneracy of the blocked, renormalized action at the gliding cutoff scale by tree-level renormalization. A quantum counterpart of this mechanism is presented in the two-dimensional sine-Gordon model. The presence of Quantum Censorship is conjectured which makes the loop contributions pile up during the renormalization and thereby realize an approximate semiclassical effect.

hep-th↗

arXiv2009

Functional renormalization group approach to the sine-Gordon model

The renormalization group flow is presented for the two-dimensional sine-Gordon model within the framework of the functional renormalization group method by including the wave-function renormalization constant. The Kosterlitz-Thouless-Berezinski type phase structure is recovered as the interpolating scaling law between two competing IR attractive area of the global renormalization group flow.

hep-th↗

arXiv2009

Turning points of massive particles in Schwarzschild geometry

The stable geodesics in Schwarzschild geometry can not approach the center closer than the radius of the photon sphere, 3/2 times the Schwarzschild radius. In other words, massive particles moving along geodesics that cross the photon sphere do not escape, they fall into the black hole.

gr-qc↗

arXiv2007

Generalized universality in the massive sine-Gordon model

A non-trivial interplay of the UV and IR scaling laws, a generalization of the universality is demonstrated in the framework of the massive sine-Gordon model, as a result of a detailed study of the global behaviour of the renormalization group flow and the phase structure.

hep-th↗

arXiv2007

Renormalizable parameters of the sine-Gordon model

The well-known phase structure of the two-dimensional sine-Gordon model is reconstructed by means of its renormalization group flow, the study of the sensitivity of the dynamics on microscopic parameters. Such an analysis resolves the apparent contradiction between the phase structure and the triviality of the effective potential in either phases, provides a case where usual classification of operators based on the linearization of the scaling relation around a fixed point is not available and shows that the Maxwell-cut generates an unusually strong universality at long distances. Possible analogies with four-dimensional Yang-Mills theories are mentioned, too.

hep-th↗

arXiv2005

Effective field theory for He-IV

We introduce an effective scalar field theory to describe the He-IV phase diagram, which can be considered as a generalization of the XY model which gives the usual lambda-transition. This theory results from a Ginzburg-Landau Hamiltonian with higher order derivatives, which allow to produce transitions between the superfluid, normal liquid and solid phases of He-IV. Mean field and Monte Carlo analyses suggest that this model is able to reproduce the main qualitative features of He-IV phase transitions.

cond-mat.other↗

arXiv2005

Running coupling constants of the Luttinger liquid

Two running coupling constants of the Luttinger liquid are computed in the fermion-fermion and fermion-antifermion channels. Nontrivial scaling laws are found together with Landau poles. The apparent contradiction with the expected vanishing of the beta functions is explained.

cond-mat.str-el↗

arXiv2004

Renormalization group in the internal space

Renormalization group in the internal space consists of the gradual change of the coupling constants. Functional evolution equations corresponding to the change of the mass or the coupling constant are presented in the framework of a scalar model. The evolution in the mass which yields the functional generalization of the Callan-Symanzik equation for the one-particle irreducible effective action is given in its renormalized, cutoff-independent form. The evolution of the coupling constant generates an evolution equation for the two-particle irreducible effective action.

hep-th↗

arXiv2004

Periodic ground state for the charged massive Schwinger model

It is shown that the charged massive Schwinger model supports a periodic vacuum structure for arbitrary charge density, similar to the common crystalline layout known in solid state physics. The dynamical origin of the inhomogeneity is identified in the framework of the bozonized model and in terms of the original fermionic variables.

hep-th↗