15,385 research outputs found
Relativistic Spheres
By analyzing the Einstein's equations for the static sphere, we find that
there exists a non-singular static configuration whose radius can approach its
corresponding horizon size arbitrarily.Comment: 8 pages revtex, 1 ps figur
Extended phase space thermodynamics for third order Lovelock black holes in diverse dimensions
Treating the cosmological constant as thermodynamic pressure and its
conjugate as thermodynamic volume, we investigate the critical behavior of the
third order Lovelock black holes in diverse dimensions. For black hole horizons
with different normalized sectional curvature , the corresponding
critical behaviors differ drastically. For , there is no critical point in
the extended thermodynamic phase space. For , there is a single critical
point in any dimension , and for , there is a single critical
point in dimension and two critical points in dimensions. We
studied the corresponding phase structures in all possible cases.Comment: pdflatex, 22 pages, 36 eps figures included. V2: minor corrections
and new reference
Gauss-Bonnet coupling constant as a free thermodynamical variable and the associated criticality
The thermodynamic phase space of Gauss-Bonnet (GB) AdS black holes is
extended, taking the inverse of the GB coupling constant as a new thermodynamic
pressure . We studied the critical behavior associated with
in the extended thermodynamic phase space at fixed
cosmological constant and electric charge. The result shows that when the black
holes are neutral, the associated critical points can only exist in five
dimensional GB-AdS black holes with spherical topology, and the corresponding
critical exponents are identical to those for Van der Waals system. For charged
GB-AdS black holes, it is shown that there can be only one critical point in
five dimensions (for black holes with either spherical or hyperbolic
topologies), which also requires the electric charge to be bounded within some
appropriate range; while in dimensions, there can be up to two different
critical points at the same electric charge, and the phase transition can occur
only at temperatures which are not in between the two critical values.Comment: 23 pages. V2: modified all P_{GB}-r_+ plots using dimensionless
variables, added comments on the relationship to Einstein limi
Age Problem in Lemaitre-Tolman-Bondi Void Models
As is well known, one can explain the current cosmic acceleration by
considering an inhomogeneous and/or anisotropic universe (which violates the
cosmological principle), without invoking dark energy or modified gravity. The
well-known one of this kind of models is the so-called
Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is
spherically symmetric and radially inhomogeneous, and we are living in a
locally underdense void centered nearby our location. In the present work, we
test various LTB void models with some old high redshift objects (OHROs).
Obviously, the universe cannot be younger than its constituents. We find that
an unusually large (characterizing the size of the void) is required to
accommodate these OHROs in LTB void models. There is a serious tension between
this unusually large and the much smaller inferred from other
observations (e.g. SNIa, CMB and so on). However, if we instead consider the
lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift , this
tension could be greatly alleviated.Comment: 17 pages, 9 figures, revtex4; v2: discussions added, Phys. Lett. B in
press; v3: published versio
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