151 research outputs found
Temperature dependence of shear viscosity of --gluodynamics within lattice simulation
In this paper we study the shear viscosity temperature dependence of
--gluodynamics within lattice simulation. To do so, we measure the
correlation functions of energy-momentum tensor in the range of temperatures
. To extract the values of shear viscosity we used two
approaches. The first one is to fit the lattice data with some physically
motivated ansatz for the spectral function with unknown parameters and then
determine shear viscosity. The second approach is to apply the Backus-Gilbert
method which allows to extract shear viscosity from the lattice data
nonparametrically. The results obtained within both approaches agree with each
other. Our results allow us to conclude that within the temperature range
SU(3)--gluodynamics reveals the properties of a strongly
interacting system, which cannot be described perturbatively, and has the ratio
close to the value in Supersymmetric Yang-Mills
theory.Comment: Typos in references are corrected and the acknowledgements are
modifie
Secularly growing loop corrections in strong electric fields
We calculate one--loop corrections to the vertexes and propagators of photons
and charged particles in the strong electric field backgrounds. We use the
Schwinger--Keldysh diagrammatic technique. We observe that photon's Keldysh
propagator receives growing with time infrared contribution. As the result,
loop corrections are not suppressed in comparison with tree--level
contribution. This effect substantially changes the standard picture of the
pair production. To sum up leading IR corrections from all loops we consider
the infrared limit of the Dyson--Schwinger equations and reduce them to a
single kinetic equation.Comment: 16 pages, no figures; Minor correction
Many-body effects in graphene beyond the Dirac model with Coulomb interaction
This paper is devoted to development of perturbation theory for studying the
properties of graphene sheet of finite size, at nonzero temperature and
chemical potential. The perturbation theory is based on the tight-binding
Hamiltonian and arbitrary interaction potential between electrons, which is
considered as a perturbation. One-loop corrections to the electron propagator
and to the interaction potential at nonzero temperature and chemical potential
are calculated. One-loop formulas for the energy spectrum of electrons in
graphene, for the renormalized Fermi velocity and also for the dielectric
permittivity are derived.Comment: 11 pages, 11 figure
Rate of cluster decomposition via Fermat-Steiner point
In quantum field theory with a mass gap correlation function between two
spatially separated operators decays exponentially with the distance. This
fundamental result immediately implies an exponential suppression of all higher
point correlation functions, but the predicted exponent is not optimal. We
argue that in a general quantum field theory the optimal suppression of a
three-point function is determined by total distance from the operator
locations to the Fermat-Steiner point. Similarly, for the higher point
functions we conjecture the optimal exponent is determined by the solution of
the Euclidean Steiner tree problem. We discuss how our results constrain
operator spreading in relativistic theories.Comment: 16 pages; journal version, appendix A adde
Study of shear viscosity of SU (2)-gluodynamics within lattice simulation
This paper is devoted to the study of two-point correlation function of the
energy-momentum tensor T_{12}T_{12} for SU(2)-gluodynamics within lattice
simulation of QCD. Using multilevel algorithm we carried out the measurement of
the correlation function at the temperature T/T_c = 1.2. It is shown that
lattice data can be described by spectral functions which interpolate between
hydrodynamics at low frequencies and asymptotic freedom at high frequencies.
The results of the study of spectral functions allowed us to estimate the ratio
of shear viscosity to the entropy density {\eta}/s = 0.134 +- 0.057.Comment: 7 pages, 3 figure
Rate of Cluster Decomposition via Fermat-Steiner Point
In quantum field theory with a mass gap correlation function between two spatially separated operators decays exponentially with the distance. This fundamental result immediately implies an exponential suppression of all higher point correlation functions, but the predicted exponent is not optimal. We argue that in a general quantum field theory the optimal suppression of a three-point function is determined by total distance from the operator locations to the Fermat-Steiner point. Similarly, for the higher point functions we conjecture the optimal exponent is determined by the solution of the Euclidean Steiner tree problem. We discuss how our results constrain operator spreading in relativistic theories
Quantum Monte Carlo study of static potential in graphene
In this paper the interaction potential between static charges in suspended
graphene is studied within the quantum Monte Carlo approach. We calculated the
dielectric permittivity of suspended graphene for the set of temperatures and
extrapolated our results to zero temperature. The dielectric permittivity at
zero temperature has the following properties. At zero distance
. Then it rises and at a large distance the dielectric
permittivity reaches the plateau . The results
obtained in this paper allow to draw a conclusion that full account of
many-body effects in the dielectric permittivity of suspended graphene gives
very close to the one-loop results. Contrary to the one-loop result,
the two-loop prediction for the dielectric permittivity deviates from our
result. So, one can expect large higher order corrections to the two-loop
prediction for the dielectric permittivity of suspended graphene.Comment: 6 pages, 2 figure
Time Evolution of Uniform Sequential Circuits
Simulating time evolution of generic quantum many-body systems using
classical numerical approaches has an exponentially growing cost either with
evolution time or with the system size. In this work, we present a polynomially
scaling hybrid quantum-classical algorithm for time evolving a one-dimensional
uniform system in the thermodynamic limit. This algorithm uses a layered
uniform sequential quantum circuit as a variational ansatz to represent
infinite translation-invariant quantum states. We show numerically that this
ansatz requires a number of parameters polynomial in the simulation time for a
given accuracy. Furthermore, this favourable scaling of the ansatz is
maintained during our variational evolution algorithm. All steps of the hybrid
optimization are designed with near-term digital quantum computers in mind.
After benchmarking the evolution algorithm on a classical computer, we
demonstrate the measurement of observables of this uniform state using a finite
number of qubits on a cloud-based quantum processing unit. With more efficient
tensor contraction schemes, this algorithm may also offer improvements as a
classical numerical algorithm.Comment: 19 pages, 14 figure
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