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Emil T. Akhmedov

Publications and source records attributed to Emil T. Akhmedov.

At least 19 recordsLinked to original sources
arXiv2024

UV Dispersive Effects on Hawking Radiation

We revisit the connection between Hawking radiation and high-frequency dispersions for a Schwarzschild black hole following the work of Brout et al.. After confirming the robustness of Hawking radiation for monotonic dispersion relations, we consider non-monotonic dispersion relations that deviate from the standard relation only in the trans-Planckian domain. Contrary to the common belief that Hawking radiation is insensitive to UV physics, it turns out that Hawking radiation is subject to significant modifications after the scrambling time. Depending on the UV physics at the singularity, the amplitude of Hawking radiation could diminish after the scrambling time, while the Hawking temperature remains the same. Our finding is thus not contradictory to earlier works regarding the robustness of Hawking temperature.

hep-th↗
arXiv2018

Ultraviolet phenomena in AdS self-interacting quantum field theory

We study the one-loop corrections to the four-point function in the Anti de Sitter space-time for a $ϕ^4$ field theory. Our calculation shows the existence of non-local counterterms which however respect the AdS isometry. Our arguments are quite general and applicable to other (non-conformal) AdS field theories. We also explain why calculations in Euclidean and Lorentzian signatures should differ even at the leading order in non globaly hyperbolic manifolds.

hep-th↗
arXiv2018

A quantum heating as an alternative of reheating

To model a realistic situation for the beginning we consider massive real scalar $ϕ^4$ theory in a (1+1)-dimensional asymptotically static Minkowski spacetime with an intermediate stage of expansion. To have an analytic headway we assume that scalars have a big mass. At past and future infinities of the background we have flat Minkowski regions which are joint by the inflationary expansion region. We use the tree-level Keldysh propagator in the theory in question to calculate the expectation value of the stress-energy tensor which is, thus, due to the excitations of the zero-point fluctuations. Then we show that even for large mass, if the de Sitter expansion stage is long enough, the quantum loop corrections to the expectation value of the stress-energy tensor are not negligible in comparison with the tree-level contribution. That is revealed itself via the excitation of the higher-point fluctuations of the exact modes: During the expansion stage a non-zero particle number density for the exact modes is generated. This density is not Plankian and serves as a quench which leads to a thermalization in the out Minkowski stage.

hep-th↗
arXiv2017

Symmetries at the black hole horizon

We determine the asymptotic symmetry group of Killing horizons by choosing Gaussian null coordinates in the neighbourhood of the horizon and boundary conditions that respect the leading order terms in the metric. The analysis divides naturally into the two cases of subextremal and extremal horizons. In general, we find rather involved asymptotic symmetry generators that nevertheless involve supertranslations and Killing vectors on the compact horizon. The most striking observation is the difference in the dependence on the coordinate along the horizon; we relate this to the redshift effect for subextremal horizons. We consider the spherically symmetric case as a special and illuminating example.

hep-th↗
arXiv2016

A way to distinguish very compact stellar objects from black holes

We propose a way to distinguish compact stellar object, whose size is very close to its Schwarzschild radius, from the collapsing stars. Namely, we show that {\it massive} fields in the vicinity of a very compact stellar object have discrete energy levels. (These levels are different from the standard non-relativistic ones present in Coulomb type of potentials and from the quasinormal modes.) At the same time we show that there are no such discrete levels for massive fields in the vicinity of a collapsing star.

gr-qc↗
arXiv2015

Hawking radiation and secularly growing loop corrections

We study the expectation value of the energy momentum tensor during thin shell collapse for a massive, real, scalar field theory. At tree-level, we find thermal, Hawking-type, behaviour for the energy flux. Using the Schwinger-Keldysh technique, we calculate two-loop corrections to the tree-level correlation functions and show that they exhibit secular growth, suggesting the breakdown of the perturbation theory.

hep-th↗
arXiv2010

Real or Imaginary? (On pair creation in de Sitter space)

Using properly defined Feynman propagator we obtain non--zero imaginary contribution to the scalar field effective action in even dimensional de Sitter space. Such a propagator follows from the path integral in de Sitter space and obeys composition principle proposed in arXiv:0709.2899. The obtained expression for the effective action shows particle production with the Gibbons--Hawking rate.

hep-th↗
arXiv2010

A simple way to take into account back reaction on pair creation

We propose a simple and systematic way of accounting for the back reaction on the background field due to the pair creation in the four--dimensional scalar QED. This method is straightforwardly generalizable to the gravity backgrounds. In the case of QED with the instantly switched on constant electric field background we obtain a remarkably simple formula for its decay rate.

hep-th↗
arXiv2010

De Sitter space and perpetuum mobile

We give general arguments that any interacting non--conformal {\it classical} field theory in de Sitter space leads to the possibility of constructing a perpetuum mobile. The arguments are based on the observation that massive free falling particles can radiate other massive particles on the classical level as seen by the free falling observer. The intensity of the radiation process is non-zero even for particles with any finite mass, i.e. with a wavelength which is within the causal domain. Hence, we conclude that either de Sitter space can not exist eternally or that one can build a perpetuum mobile.

gr-qc↗
arXiv2008

Subtleties in the quasi-classical calculation of Hawking radiation

he quasi-classical method of deriving Hawking radiation is investigated. In order to recover the original Hawking temperature one must take into account a previously ignored contribution coming from the temporal part of the action. This contribution plus a contribution coming from the spatial part of the action gives the correct temperature.

gr-qc↗
arXiv2008

Interacting Field Theories in de Sitter Space are Non-Unitary

It is well known that there should be a total cancellation of the IR divergences in unitary interacting field theories, such as QED and gravity. The cancellation should be at all orders between loop and tree level contributions to cross--sections. This is the crucial fact related to the unitarity of the evolution operator (S--matrix) of the underlying interacting field theory. In this note we show that such a cancellation does {\it not} happen in de Sitter space.

hep-th↗
arXiv2007

On the physical meaning of the Unruh effect

We present simple arguments that detectors moving with constant acceleration (even acceleration for a finite time) should detect particles. The effect is seen to be universal. Moreover, detectors undergoing linear acceleration and uniform, circular motion both detect particles for the same physical reason. We show that if one uses a circularly orbiting electron in a constant external magnetic field as the Unruh--DeWitt detector, then the Unruh effect physically coincides with the experimentally verified Sokolov--Ternov effect.

hep-th↗
arXiv2007

On the relation between Unruh and Sokolov--Ternov effects

We show that the Sokolov--Ternov effect -- the depolarization of particles in storage rings coming from synchrotron radiation due to spin flip transitions -- is physically equivalent to the Unruh effect for circular acceleration if one uses a spin 1/2 particle as the Unruh--DeWitt detector. It is shown that for the electron, with gyromagnetic number $g \approx 2$, the exponential contribution to the polarization, which usually characterizes the Unruh effect, is "hidden" in the standard Sokolov-Ternov effect making it hard to observe. Thus, our conclusions are different in detail from previous work.

hep-ph↗
arXiv2007

Thermal radiation of various gravitational backgrounds

We present a simple and general procedure for calculating the thermal radiation coming from any stationary metric. The physical picture is that the radiation arises as the quasi--classical tunneling of particles through a gravitational barrier. We show that our procedure can reproduce the results of Hawking and Unruh radiation. We also show that under certain kinds of coordinate transformations the temperature of the thermal radiation will change in the case of the Schwarzschild black holes. In addition we apply our procedure to a rotating/orbiting system and show that in this case there is no radiation, which has experimental implications for the polarization of particles in circular accelerators.

hep-th↗
arXiv2006

Hawking temperature in the tunneling picture

We examine Hawking radiation from a Schwarzschild black hole in several reference frames using the quasi-classical tunneling picture. It is shown that when one uses, $Γ\propto \exp(Im [\oint p dr])$, rather than, $Γ\propto \exp(2 Im [\int p dr])$, for the tunneling probability/decay rate one obtains twice the original Hawking temperature. The former expression for $Γ$ is argued to be correct since $\oint p dr$ is invariant under canonical transformations, while $\int p dr$ is not. Thus, either the tunneling methods of calculating Hawking radiation are suspect or the Hawking temperature is twice that originally calculated.

hep-th↗