33,727 research outputs found
Global Scaling Symmetry, Noether Charge and Universality of Shear Viscosity
Recently it was established in Einstein-Maxwell-Dilaton gravity that the KSS
viscosity/entropy ratio associated with AdS planar black holes can be viewed as
the boundary dual to the generalized Smarr relation of the black holes in the
bulk. In this paper we establish this relation in Einstein gravity with general
minimally-coupled matter, and also in theories with an additional non-minimally
coupled scalar field. We consider two examples for explicit demonstrations.Comment: 16 pages, no figur
Lifshitz and Schrodinger Vacua, Superstar Resolution in Gauged Maximal Supergravities
We consider the subset of gauged maximal supergravities that consists of the
SO(n+1) gauge fields A^{ij} and the scalar deformation T^{ij} of the S^n in the
spherical reduction of M-theory or type IIB. We focus on the Abelian Cartan
subgroup and the diagonal entries of T^{ij}. The resulting theories can be
viewed as the STU models with additional hyperscalars. We find that the
theories with only one or two such vectors can be generalized naturally to
arbitrary dimensions. The same is true for the D=4 or 5 Einstein-Maxwell theory
with such a hyperscalar. The gauge fields become massive, determined by
stationary points of the hyperscalars a la the analogous Abelian Higgs
mechanism. We obtain classes of Lifshitz and Schrodinger vacua in these
theories. The scaling exponent z turns out to be rather restricted, taking
fractional or irrational numbers. Tweaking the theories by relaxing the mass
parameter or making a small change of the superpotential, we find that
solutions with z=2 can emerge. In a different application, we find that the
resolution of superstar singularity in the STU models by using bubbling-AdS
solitons can be generalized to arbitrary dimensions in our theories. In
particular, we obtain the smooth AdS solitons that can be viewed as the
resolution of the Reissner-Nordstrom superstars in general dimensions.Comment: Latex, 24 page
Thermodynamics of Lifshitz Black Holes
We specialize the Wald formalism to derive the thermodynamical first law for
static black holes with spherical/torus/hyperbolic symmetries in a variety of
supergravities or supergravity-inspired theories involving multiple scalars and
vectors. We apply the formula to study the first law of a general class of
Lifshitz black holes. We analyse the first law of three exact Lifshitz black
holes and the results fit the general pattern. In one example, the first law is
where are the electric potential and charge of the
Maxwell field. The unusual vanishing of mass in this specific solution
demonstrates that super-extremal charged black holes can exist in asymptotic
Lifshitz spacetimes.Comment: 27 page
Scalar Charges in Asymptotic AdS Geometries
We show that for n-dimensional Einstein gravity coupled to a scalar field
with mass-squared m_0^2=-n(n-2)/(4\ell^2), the first law of thermodynamics of
(charged) AdS black holes will be modified by the boundary conditions of the
scalar field at asymptotic infinity. Such scalars can arise in gauged
supergravities in four and six dimensions, but not in five or seven. The result
provides a guiding principle for constructing designer black holes and solitons
in general dimensions, where the properties of the dual field theories depend
on the boundary conditions.Comment: Latex, 9 pages, references adde
Blue Phosphorene Oxide: Strain-tunable Quantum Phase Transitions and Novel 2D Emergent Fermions
Tunable quantum phase transitions and novel emergent fermions in solid state
materials are fascinating subjects of research. Here, we propose a new stable
two-dimensional (2D) material, the blue phosphorene oxide (BPO), which exhibits
both. Based on first-principles calculations, we show that its equilibrium
state is a narrow-bandgap semiconductor with three bands at low energy.
Remarkably, a moderate strain can drive a semiconductor-to-semimetal quantum
phase transition in BPO. At the critical transition point, the three bands
cross at a single point at Fermi level, around which the quasiparticles are a
novel type of 2D pseudospin-1 fermions. Going beyond the transition, the system
becomes a symmetry-protected semimetal, for which the conduction and valence
bands touch quadratically at a single Fermi point that is protected by
symmetry, and the low-energy quasiparticles become another novel type of 2D
double Weyl fermions. We construct effective models characterizing the phase
transition and these novel emergent fermions, and we point out several exotic
effects, including super Klein tunneling, supercollimation, and universal
optical absorbance. Our result reveals BPO as an intriguing platform for the
exploration of fundamental properties of quantum phase transitions and novel
emergent fermions, and also suggests its great potential in nanoscale device
applications.Comment: 23 pages, 5 figure
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