98 research outputs found
Shock waves in Lifshitz-like spacetimes
We construct shock waves for Lifshitz-like geometries in four- and
five-dimensional effective theories as well as in D3-D7 and D4-D6 brane
systems. The solutions to the domain wall profile equations are found. Further,
the study makes a connection with the implications for the quark-gluon plasma
formation in heavy-ion collisions. According to the holographic approach, the
multiplicity of particles produced in heavy-ion collisions can be estimated by
the area of the trapped surface formed in shock wave collisions. We calculate
the areas of trapped surfaces in the geometry of two colliding Lifshitz domain
walls. Our estimates show that for five-dimensional cases with certain values
of the critical exponent the dependence of multiplicity on the energy of
colliding ions is rather close to the experimental data observed at RHIC and LHC.Comment: 35 pages, 6 figures; v3: typos corrected. Version to appear in JHE
Exact solutions in gravity with a sigma model source
We consider a D-dimensional model of gravity with non-linear "scalar fields"
as a matter source. The model is defined on the product manifold M, which
contains n Einstein factor spaces. General cosmological type solutions to the
field equations are obtained when n-1 factor spaces are Ricci-flat, e.g. when
one space M_1 of dimension d_1 > 1 has nonzero scalar curvature. The solutions
are defined up to solutions to geodesic equations corresponding to a sigma
model target space. Several examples of sigma models are presented. A subclass
of spherically-symmetric solutions is studied and a restricted version of
"no-hair theorem" for black holes is proved. For the case d_1 =2 a subclass of
latent soliton solutions is singled out.Comment: 22 pages, Latex, several phrases and 4 refs. are addes, few typos are
eliminate
Elliptic solutions of generalized Brans-Dicke gravity with a non-universal coupling
We study a model of the generalized Brans-Dicke gravity presented in both the
Jordan and in the Einstein frames, which are conformally related. We show that
the scalar field equations in the Einstein frame are reduced to the geodesics
equations on the target space of the nonlinear sigma-model. The analytical
solutions in elliptical functions are obtained when the conformal couplings are
given by reciprocal exponential functions. The behavior of the scale factor in
the Jordan frame is studied using numerical computations. For certain
parameters the solutions can describe an accelerated expansion. We also derive
an analytical approximation in exponential functions.Comment: 24 pages, 3 figures; v2: typos fixed, few remarks and references
added; version to appear in EPJ
Analytic black branes in Lifshitz-like backgrounds and thermalization
Using black brane solutions in 5d Lifshitz-like backgrounds with arbitrary
dynamical exponent , we construct the Vaidya geometry, asymptoting to the
Lifshitz-like spacetime, which represents a thin shell infalling at the speed
of light. We apply the new Lifshitz-Vaidya background to study the
thermalization process of the quark-gluon plasma via the thin shell approach
previously successfully used in several backgrounds. We find that the
thermalization depends on the chosen direction because of the spatial
anisotropy. The plasma thermalizes thus faster in the transversal direction
than in the longitudinal one. To probe the system described by the
Lifshitz-like backgrounds, we also calculate the holographic entanglement
entropy for the subsystems delineated along both transversal and longitudinal
directions. We show that the entropy has some universality in the behavior for
both subsystems. At the same time, we find that certain characteristics
strongly depend on the critical exponent .Comment: 39 pages, 23 figures; v3: typos corrected, references and
clarifications added, version published in JHE
Thermalization of holographic Wilson loops in spacetimes with spatial anisotropy
In this paper, we study behaviour of Wilson loops in the boost-invariant
nonequilibrium anisotropic quark-gluon plasma produced in heavy-ion collisions
within the holographic approach. We describe the thermalization studying the
evolution of the Vaidya metric in the boost-invariant and spatially anisotropic
background. To probe the system during this process we calculate rectangular
Wilson loops oriented in different spatial directions. We find that anisotropic
effects are more visible for the Wilson loops lying in the transversal plane
unlike the Wilson loops with partially longitudinal orientation. In particular,
we observe that the Wilson loops can thermalizes first unlike to the order of
the isotropic model. We see that Wilson loops on transversal contours have the
shortest thermalization time. We also calculate the string tension and the
pseudopotential at different temperatures for the static quark-gluon plasma. We
show that the pseudopotential related to the configuration on the transversal
plane has the screened Cornell form. We also show that the jet-quenching
parameter related with the average of the light-like Wilson loop exhibits the
dependence on orientations.Comment: 39 pages, 12 figures; v3: typos corrected, to appear in Nucl. Phys.
Probing the holographic model of SYM rotating quark-gluon plasma
We study Wilson loops in holographic duals of the SYM
quark-gluon plasma. For this we consider the Schwarzschild- and
Kerr- black holes, which are dual to the non-rotating and rotating QGPs,
correspondingly. From temporal Wilson loops we find the heavy quark potentials
in both backgrounds. For the temperature above the critical temperature we
observe the Coulomb-like behavior of the potentials. We find that increasing
the rotation the interquark distance decreases, we also see that the increase
of the temperature yields the similar behavior. Moreover, at high temperatures
for certain values of parameters the potentials in Schwarzschild- and
Kerr- are close to that one calculated in the AdS black brane with a
planar horizon. We also explore holographic light-like Wilson-loops from which
the jet-quenching parameters of a fast parton are extracted. We find that the
rotation increases the value of the jet-quenching parameter. However, at high
temperatures the jet-quenching parameters have a cubic dependence on the
temperature as for the the AdS black brane.Comment: 32 pp, 11 fig
Stability analysis of holographic RG flows in 3d supergravity
We study holographic RG flows in a 3d supergravity model from the side of the
dynamical system theory. The gravity equations of motion are reduced to an
autonomous dynamical system.
Then we find equilibrium points of the system and analyze them for stability.
We also restore asymptotic solutions near the critical points. We find two
types of solutions: with asymptotically AdS metrics and hyperscaling violating
metrics. We write down possible RG flows between an unstable (saddle) UV fixed
point and a stable (stable node) IR fixed point. We also analyze bifurcations
in the model.Comment: 26 pp., 7 figure
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