5,877 research outputs found

### Stationary strings near a higher-dimensional rotating black hole

We study stationary string configurations in a space-time of a
higher-dimensional rotating black hole. We demonstrate that the Nambu-Goto
equations for a stationary string in the 5D Myers-Perry metric allow a
separation of variables. We present these equations in the first-order form and
study their properties. We prove that the only stationary string configuration
which crosses the infinite red-shift surface and remains regular there is a
principal Killing string. A worldsheet of such a string is generated by a
principal null geodesic and a timelike at infinity Killing vector field. We
obtain principal Killing string solutions in the Myers-Perry metrics with an
arbitrary number of dimensions. It is shown that due to the interaction of a
string with a rotating black hole there is an angular momentum transfer from
the black hole to the string. We calculate the rate of this transfer in a
spacetime with an arbitrary number of dimensions. This effect slows down the
rotation of the black hole. We discuss possible final stationary configurations
of a rotating black hole interacting with a string.Comment: 13 pages, contains additianal material at the end of Section 8, also
small misprints are correcte

### Non-linear Dynamics and Primordial Curvature Perturbations from Preheating

In this paper I review the theory and numerical simulations of non-linear
dynamics of preheating, a stage of dynamical instability at the end of
inflation during which homogeneous inflaton explosively decays and deposits its
energy into excitation of other matter fields. I focus on preheating in chaotic
inflation models, which proceeds via broad parametric resonance. I describe a
simple method to evaluate Floquet exponents, calculating stability diagrams of
Mathieu and Lame equations describing development of instability in $m^2\phi^2$
and $\lambda\phi^4$ preheating models. I discuss basic numerical methods and
issues, and present simulation results highlighting non-equilibrium
transitions, topological defect formation, late-time universality, turbulent
scaling and approach to thermalization. I explain how preheating can generate
large-scale primordial (non-Gaussian) curvature fluctuations manifest in cosmic
microwave background anisotropy and large scale structure, and discuss
potentially observable signatures of preheating.Comment: 15 pages, 10 figures; review for CQG special issu

### Semi-inclusive charged-pion electroproduction off protons and deuterons: Cross sections, ratios, and access to the quark-parton model at low energies

A large set of cross sections for semi-inclusive electroproduction of charged pions (π^±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W^2>4 GeV^2 (up to ≈7 GeV^2) and range in four-momentum transfer squared 2<Q^2<4 (GeV/c)^2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt^(2)_(t)<0.2 (GeV/c)2. The invariant mass that goes undetected, M_x or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt^(2)_(t) dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π^+ and π^−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths

### Applications of hidden symmetries to black hole physics

This work is a brief review of applications of hidden symmetries to black
hole physics. Symmetry is one of the most important concepts of the science. In
physics and mathematics the symmetry allows one to simplify a problem, and
often to make it solvable. According to the Noether theorem symmetries are
responsible for conservation laws. Besides evident (explicit) spacetime
symmetries, responsible for conservation of energy, momentum, and angular
momentum of a system, there also exist what is called hidden symmetries, which
are connected with higher order in momentum integrals of motion. A remarkable
fact is that black holes in four and higher dimensions always possess a set
(`tower') of explicit and hidden symmetries which make the equations of motion
of particles and light completely integrable. The paper gives a general review
of the recently obtained results. The main focus is on understanding why at all
black holes have something (symmetry) to hide.Comment: This is an extended version of the talks at NEB-14 conference
(June,Ioannina,Greece) and JGRG20 meeting (September, Kyoto, Japan

### Statistical Mechanics of Charged Black Holes in Induced Einstein-Maxwell Gravity

The statistical origin of the entropy of charged black holes in models of
induced Einstein-Maxwell gravity is investigated. The constituents inducing the
Einstein-Maxwell action are charged and interact with an external gauge
potential. This new feature, however, does not change divergences of the
statistical-mechanical entropy of the constituents near the horizon. It is
demonstrated that the mechanism of generation of the Bekenstein-Hawking entropy
in induced gravity is universal and it is basically the same for charged and
neutral black holes. The concrete computations are carried out for induced
Einstein-Maxwell gravity with a negative cosmological constant in three
space-time dimensions.Comment: 16 pages, latex, no figure

### Scattering of Straight Cosmic Strings by Black Holes: Weak Field Approximation

The scattering of a straight, infinitely long string moving with velocity $v$
by a black hole is considered. We analyze the weak-field case, where the impact
parameter ($b_{imp}$) is large, and obtain exact solutions to the equations of
motion. As a result of scattering, the string is displaced in the direction
perpendicular to the velocity by an amount $\Delta b\sim -2\pi GMv\gamma/c^3
-\pi (GM)^2/ (4c^3 v b_{imp})$, where $\gamma=(1-(v/c)^2)^{-1/2}$. The second
term dominates at low velocities $v/c<(GM/b_{imp})^{1/2}$ . The late-time
solution is represented by a kink and anti-kink, propagating in opposite
directions at the speed of light, and leaving behind them the string in a new
``phase''. The solutions are applied to the problem of string capture, and are
compared to numerical results.Comment: 19 pages, 5 figure

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