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D. V. Diakonov

Publications and source records attributed to D. V. Diakonov.

12 recordsLinked to original sources
arXiv2026

Soliton like solutions of $λϕ^4$ theory in de Sitter space

We study classical solutions of a scalar field with quartic potential in de Sitter space-time. Using the ansatz $ϕ=F(X\cdotξ)$, via embeding coordinate $X_α$ of the ambiend space we find several families of analytic solutions classified by the causal character of the constant vector $ξ$. For time-like $ξ$, the solutions are globally regular and describe either global oscillations around a minimum or global vacuum transition; for space-like $ξ$, they are singular in the global patch but regular in the open slicing. In the Poincaré patch they correspond to contracting bubbles. We compute the classical actions of these solition which are finite only in spacetime dimensions $D \le 5$. We show that the $D=4$ global vacuum transition solution has the radiation equation of state $w=1/3$. In $D=4$ global vacuum transition solution, the retarded Green's function acquires a growing tail as compared to the Green's function on top of vacuum, implying that the transition amplifies the signal at late times.

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arXiv2026

One more Sine-Gordon soliton in AdS

In previous work arXiv:2604.00160, we found soliton solutions in a deformation of the sine-Gordon theory in AdS spacetime that, in the infinite-radius limit, reduce to single-soliton solutions in flat space. In this paper, we find another single soliton solution that has no analog in flat space.

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arXiv2026

Sine-Gordon solitons in AdS, dS and other hyperbolic spaces

We find infinitely many soliton-like solutions in a deformation of the sine-Gordon theory in $(d+1)$-dimensional $AdS_{d+1}$ (anti-de Sitter) spacetime for $d \geq 2$, as well as single solitonic solutions in $dS_{d+1}$ (de Sitter) and $\mathrm{H}{d+1}$ (Lobachevsky) spaces for $d \geq 1$ and in $AdS_2$. We also find a deformation of the kink solution in scalar field theory with a polynomial potential in $AdS_2$. The deformation of the sine-Gordon theory strikingly resembles the bosonic part of the flat-space supersymmetric sine-Gordon theory. In the infinite radius limit, single soliton solutions reduce to solitons in flat space. Meanwhile, the multisoliton solution of $AdS{d+1}$, $d\geq 2$ for certain values of the parameters reduces in the same limit to a single soliton solution boosted in the normal direction. However, there are also multisoliton solutions in $AdS_{d+1}$, $d \geq 2$ that do not have a flat space limit.

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arXiv2025

Lessons from the Klein paradox

We re-examine the Klein paradox from a many-particle perspective in quantum field theory. Specifically, we compute the expectation value of the particle current induced by a sufficiently strong step-like electric potential in 1+1 dimensions. First, for a constant (eternal) potential, we calculate the current for different Fock space ground states corresponding to distinct mode bases. While one basis yields a zero current, another produces the standard nonzero value. We then consider a potential that is rapidly switched on, recovering the standard current in the asymptotic future. This result is generalized to potentials that interpolate between different constant values at spatial infinity. Finally, we analyze a potential acting for a finite duration and again reproduce the standard current. A physical interpretation of these results is provided.

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arXiv2024

On (dis)agreement between different methods of calculation of the imaginary part of the effective action in expanding space-times

We consider two approaches to calculate imaginary parts of effective actions in expanding space-times. While the first approach uses Bogolyubov coefficients, the second one uses the functional integral or the Feynman propagator. In eternally expanding space-times these two approaches give different answers for the imaginary parts. The origin of the difference can be traced to the presence if the wave-functionals for the initial and final states in the functional integral. We show this explicitly on the example of the expanding Poincare patch of the de Sitter space-time.

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arXiv2023

Thermal loops in the accelerating frame

We consider the conformal scalar field theory with $λϕ^4$ self-interaction in Rindler and Minkowskian coordinates at finite temperature planckian distribution for the exact modes. The solution of the one-loop Dyson-Schwinger equation is found to the order in $λ^{3/2}$. Appearance of the thermal (Debye) mass is shown. Unlike the physical mass, the thermal one gives a gap in the energy spectrum in the quantization in the Rindler coordinates. The difference between such calculations in Minkowski and Rindler coordinates for the exact modes is discussed. It is also shown that states with a temperature lower than the Unruh one are unstable. It is proved that for the canonical Unruh temperature the thermal mass is equal to zero. The contribution to the quantum average of the stress-energy tensor is also calculated, it remains traceless even in the presence of the thermal mass.

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arXiv2022

Free energy and entropy in Rindler and de Sitter space-times

We investigate the free energy and entropy of the Gaussian massive scalar field theory in the static de Sitter space-time for arbitrary temperature. For the inverse temperatures of the form $β=2 π2^k, \ \ k\in \mathbf{Z}$, in curvature units, we find the explicit form of the free energy and its derivatives with respect to the temperature. There are two types of contributions to the free energy: one is of the "area type" and can be attributed to the horizon, while the other is of the "volume type" and is associated with the interior of the space-time. The latter contribution in the odd-dimensional case in the limit of the week field (large mass or small Hubble constant) significantly depends on the temperature. Namely, for $ β<2π$, the free energy behaves as $ F^{bulk}_β \sim e^{- β\, m} $, while for $β>2π$ it behaves as $ F^{bulk}_β \sim e^{- 2 \, π\, m}$. We also show that even the leading UV contributions to the free energy significantly depend on the state of the theory, which is very unusual. We explain the origin and physical meaning of these observations. As the model example we consider the situation in the Rindler wedge of the flat space-time.

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arXiv2021

Quantum fields in the future Rindler wedge

We consider interacting massive scalar quantum field theory in the future Rindler wedge. This is a model example of quantum field theory in curved space--time. On this simple example we show how dynamics of correlation functions depends on the choice of initial Cauchy surface, basis of modes and on the choice of initial state build with the use of the corresponding creation and annihilation operators. We show which choice of modes in the future Rindler wedge respects Poincare symmetry. But we do not restrict our attention only to these modes and the corresponding state.

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arXiv2021

Heating up an environment around black holes and inside de Sitter space

We study quantum fields on spacetimes having a bifurcate Killing horizon by allowing the possibility that left- and right- (in-going and out-going) modes have different temperatures. We consider in particular the Rindler for both massless and massive fields, the static de Sitter and Schwarzschild black hole backgrounds for massive fields. We find that in all three cases, when any of the temperatures is different from the canonical one (Unruh, Hawking and Gibbons--Hawking, correspondingly) the correlation functions have extra singularities at the horizon.

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arXiv2020

Quantum fields in the static de Sitter universe

We construct explicit mode expansions of various tree-level propagators in the Rindler -- de Sitter universe, also known as the static (or compact) patch of the de Sitter spacetime. We construct in particular the Wightman functions for thermal states having a generic temperature $T$. We give a fresh simple proof that the only thermal Wightman propagator that respects the de Sitter isometry is the restriction to the Rindler -- de Sitter wedge of the propagator for the Bunch--Davies state. It is the thermal state with $T = (2 π)^{-1}$ in the units of de Sitter curvature. We show that propagators with $T\ne(2π)^{-1}$ are only time translation invariant and have extra singularities on the boundary of the static patch. We also construct the expansions for the so-called alpha-vacua in the static patch and discuss the flat limit.

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arXiv2019

Propagators and Gaussian effective actions in various patches of de Sitter space

We consider time-ordered (or Feynman) propagators between two different $α-$states of a linear de Sitter Quantum Field in the global de Sitter manifold and in the Poincaré patch. We separately examine $α-β$, In-In and In-Out propagators and find the imaginary contribution to the effective actions. The In-In propagators are real in both the Poincaré patch and in the global de Sitter manifold. On the other side the In-Out propagators at coincident points contain finite imaginary contributions in both patches in even dimensions, but they are not equivalent. In odd dimensions in both patches the imaginary contributions are zero. For completeness, we also consider the Static patch and identify in our construction the state that is equivalent to the Bunch-Davies one in the Poincaré patch.

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