20 research outputs found
Lifshitz black holes in string theory
We provide the first black hole solutions with Lifshitz asymptotics found in
string theory. These are expected to be dual to models enjoying anisotropic
scale invariance with dynamical exponent z=2 at finite temperature. We employ a
consistent truncation of type IIB supergravity to four dimensions with an
arbitrary 5-dimensional Einstein manifold times a circle as internal geometry.
New interesting features are found that significantly differ from previous
results in phenomenological models. In particular, small black holes are shown
to be thermodynamically unstable, analogously to the usual AdS-Schwarzschild
black holes, and extremality is never reached. This signals a possible
Hawking-Page like phase transition at low temperatures.Comment: 19 pages, 7 figures. v2 references adde
Shaping black holes with free fields
Starting from a metric Ansatz permitting a weak version of Birkhoff's theorem
we find static black hole solutions including matter in the form of free scalar
and p-form fields, with and without a cosmological constant \Lambda. Single
p-form matter fields permit multiple possibilities, including dyonic solutions,
self-dual instantons and metrics with Einstein-Kaelher horizons. The inclusion
of multiple p-forms on the other hand, arranged in a homogeneous fashion with
respect to the horizon geometry, permits the construction of higher dimensional
dyonic p-form black holes and four dimensional axionic black holes with flat
horizons, when \Lambda<0. It is found that axionic fields regularize black hole
solutions in the sense, for example, of permitting regular -- rather than
singular -- small mass Reissner-Nordstrom type black holes. Their cosmic string
and Vaidya versions are also obtained.Comment: 38 pages. v2: minor changes, published versio
Holographic Superconductors
A holographic model of superconductors based on the action proposed by
Benini, Herzog, and Yarom [arXiv:1006.0731] is studied. This model has a
charged spin two field in an AdS black hole spacetime. Working in the probe
limit, the normalizable solution of the spin two field in the bulk gives rise
to a superconducting order parameter at the boundary of the AdS. We
calculate the fermion spectral function in this\ superconducting background and
confirm the existence of fermi arcs for non-vanishing Majorana couplings. By
changing the relative strength of the and condensations, the
position and the size of the fermi arcs are changed. When , the
spectrum becomes isotropic and the spectral function is s-wave like. By
changing the fermion mass, the fermi momentum is changed. We also calculate the
conductivity for these holographic superconductors where time reversal
symmetry has been broken spontaneously. A non-vanishing Hall conductivity is
obtained even without an external magnetic field.Comment: 24 pages,17 figures, Add more discussions on hall conductivity, two
new figures, Matched with published versio
Holography of Charged Dilaton Black Holes
We study charged dilaton black branes in . Our system involves a
dilaton coupled to a Maxwell field with dilaton-dependent
gauge coupling, . First, we find the solutions for
extremal and near extremal branes through a combination of analytical and
numerical techniques. The near horizon geometries in the simplest cases, where
, are Lifshitz-like, with a dynamical exponent
determined by . The black hole thermodynamics varies in an interesting
way with , but in all cases the entropy is vanishing and the specific
heat is positive for the near extremal solutions. We then compute conductivity
in these backgrounds. We find that somewhat surprisingly, the AC conductivity
vanishes like at T=0 independent of . We also explore the
charged black brane physics of several other classes of gauge-coupling
functions . In addition to possible applications in AdS/CMT, the
extremal black branes are of interest from the point of view of the attractor
mechanism. The near horizon geometries for these branes are universal,
independent of the asymptotic values of the moduli, and describe generic
classes of endpoints for attractor flows which are different from .Comment: 33 pages, 3 figures, LaTex; v2, references added; v3, more refs
added; v4, refs added, minor correction
New AdS solitons and brane worlds with compact extra-dimensions
We construct new static, asymptotically AdS solutions where the conformal
infinity is the product of Minkowski spacetime and a sphere . Both
globally regular, soliton-type solutions and black hole solutions are
considered. The black holes can be viewed as natural AdS generalizations of the
Schwarzschild black branes in Kaluza-Klein theory. The solitons provide new
brane-world models with compact extra-dimensions. Different from the
Randall-Sundrum single-brane scenario, a Schwarzschild black hole on the Ricci
flat part of these branes does not lead to a naked singularity in the bulk.Comment: 28 pages, 4 figure
Towards strange metallic holography
We initiate a holographic model building approach to `strange metallic'
phenomenology. Our model couples a neutral Lifshitz-invariant quantum critical
theory, dual to a bulk gravitational background, to a finite density of gapped
probe charge carriers, dually described by D-branes. In the physical regime of
temperature much lower than the charge density and gap, we exhibit anomalous
scalings of the temperature and frequency dependent conductivity. Choosing the
dynamical critical exponent appropriately we can match the non-Fermi liquid
scalings, such as linear resistivity, observed in strange metal regimes. As
part of our investigation we outline three distinct string theory realizations
of Lifshitz geometries: from F theory, from polarised branes, and from a
gravitating charged Fermi gas. We also identify general features of
renormalisation group flow in Lifshitz theories, such as the appearance of
relevant charge-charge interactions when . We outline a program to
extend this model building approach to other anomalous observables of interest
such as the Hall conductivity.Comment: 71 pages, 8 figure
Brane effective actions, kappa-symmetry and applications
This is a review on brane effective actions, their symmetries and some of their applications. Its first part covers the Green–Schwarz formulation of single M- and D-brane effective actions focusing on kinematical aspects: the identification of their degrees of freedom, the importance of world volume diffeomorphisms and kappa symmetry to achieve manifest spacetime covariance and supersymmetry, and the explicit construction of such actions in arbitrary on-shell supergravity backgrounds. Its second part deals with applications. First, the use of kappa symmetry to determine supersymmetric world volume solitons. This includes their explicit construction in flat and curved backgrounds, their interpretation as Bogomol’nyi–Prasad–Sommerfield (BPS) states carrying (topological) charges in the supersymmetry algebra and the connection between supersymmetry and Hamiltonian BPS bounds. When available, I emphasise the use of these solitons as constituents in microscopic models of black holes. Second, the use of probe approximations to infer about the non-trivial dynamics of strongly-coupled gauge theories using the anti de Sitter/conformal field theory (AdS/CFT) correspondence. This includes expectation values of Wilson loop operators, spectrum information and the general use of D-brane probes to approximate the dynamics of systems with small number of degrees of freedom interacting with larger systems allowing a dual gravitational description. Its final part briefly discusses effective actions for N D-branes and M2-branes. This includes both Super-Yang-Mills theories, their higher-order corrections and partial results in covariantising these couplings to curved backgrounds, and the more recent supersymmetric Chern–Simons matter theories describing M2-branes using field theory, brane constructions and 3-algebra considerations