2,150 research outputs found
Relativistic gyratons in asymptotically AdS spacetime
We study the gravitational field of a spinning radiation beam-pulse (a
gyraton) in a D-dimensional asymptotically AdS spacetime. It is shown that the
Einstein equations for such a system reduce to a set of two linear equations in
a (D-2)-dimensional space. By solving these equations we obtain a metric which
is an exact solution of gravitational equations with the (negative)
cosmological constant. The explicit metrics for 4D and 5D gyratons in
asymptotically AdS spacetime are given and their properties are discussed.Comment: 10 page
Polarization Charge Distribution in Gapped Graphene
We study the distribution of vacuum polarization charge induced by a Coulomb
impurity in massive graphene. By analytically computing the polarization
function, we show that the charge density is distributed in space in a
non-trivial fashion, and on a characteristic length-scale set by the effective
Compton wavelength. The density crosses over from a logarithmic behavior below
this scale, to a power law variation above it. Our results in the continuum
limit are confirmed by explicit diagonalization of the corresponding
tight-binding model on a finite-size lattice. Electron-electron interaction
effects are also discussed.Comment: 6 pages, 4 figures; expanded versio
`Hidden' Symmetries of Higher Dimensional Rotating Black Holes
We demonstrate that the rotating black holes in an arbitrary number of
dimensions and without any restrictions on their rotation parameters possess
the same `hidden' symmetry as the 4-dimensional Kerr metric. Namely, besides
the spacetime symmetries generated by the Killing vectors they also admit the
(antisymmetric) Killing-Yano and symmetric Killing tensors.Comment: 4 pages, slightly extended introductio
String Gyratons in Supergravity
We study solutions of the supergravity equations with the string-like sources
moving with the speed of light. An exact solution is obtained for the
gravitational field of a boosted ring string in any dimension greater than
three.Comment: 7 pages;v2 minor changes & references added, final in PR
Particle Dynamics in Weakly Charged Extreme Kerr Throat
We study dynamics of a test charged particle moving in a weakly charged
extreme Kerr throat. Dynamical equations of the particle motion are solved in
quadratures. We show explicitly that the Killing tensor of the Kerr spacetime
becomes reducible in the extreme Kerr throat geometry. Special types of motion
of particles and light are discussed.Comment: The paper is prepared for the fest volume devoted to 75th Birthday of
Mario Castagnin
Observable form of pulses emitted from relativistic collapsing objects
In this work, we discuss observable characteristics of the radiation emitted
from a surface of a collapsing object. We study a simplified model in which a
radiation of massless particles has a sharp in time profile and it happens at
the surface at the same moment of comoving time. Since the radiating surface
has finite size the observed radiation will occur during some finite time. Its
redshift and bending angle are affected by the strong gravitational field. We
obtain a simple expression for the observed flux of the radiation as a function
of time. To find an explicit expression for the flux we develop an analytical
approximation for the bending angle and time delay for null rays emitted by a
collapsing surface. In the case of the bending angle this approximation is an
improved version of the earlier proposed Beloborodov-Leahy-approximation. For
rays emitted at the accuracy of the proposed improved approximations
for the bending angle and time delay is of order (or less) than 2-3%. By using
this approximation we obtain an approximate analytical expression for the
observed flux and study its properties.Comment: 13 pages, 10 figures;Typos in equations and refrences are corrected.
No change in the results and discussion
Electron-Electron Interactions in the Vacuum Polarization of Graphene
We discuss the effect of electron-electron interactions on the static
polarization properties of graphene beyond RPA. Divergent self-energy
corrections are naturally absorbed into the renormalized coupling constant
. We find that the lowest order vertex correction, which is the first
non-trivial correlation contribution, is finite, and about 30% of the RPA
result at strong coupling . The vertex correction leads to
further reduction of the effective charge. Finite contributions to dielectric
screening are expected in all orders of perturbation theory.Comment: 5 pages, 2 figures; published versio
Stability of the spiral phase in the 2D extended t-J model
We analyze the t-t'-t''-J model at low doping by chiral perturbation theory
and show that the (1,0) spiral state is stabilized by the presence of t',t''
above critical values around 0.2J, assuming t/J=3.1. We find that the (magnon
mediated) hole-hole interactions have an important effect on the region of
charge stability in the space of parameters t',t'', generally increasing
stability, while the stability in the magnetic sector is guaranteed by the
presence of spin quantum fluctuations (order from disorder effect). These
conclusions are based on perturbative analysis performed up to two loops, with
very good convergence.Comment: 7 pages, 6 figure
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