128 research outputs found

### Gauging Conformal Algebras with Relations between the Generators

We investigate the gauging of conformal algebras with relations between the
generators. We treat the $W_{5/2}$--algebra as a specific example. We show that
the gauge-algebra is in general reducible with an infinite number of stages. We
show how to construct the BV-extended action, and hence the classical BRST
charge. An important conclusion is that this can always be done in terms of the
generators of the $W$--algebra only, that is, independent of the realisation.
The present treatment is still purely classical, but already enables us to
learn more about reducible gauge algebras and the BV-formalism.Comment: 10 pages, LaTex, This paper is based on proceedings for the Sixth
Seminar on Quantum Gravity, Moscow, 12-17 June '95 and the Conference on
Gauge theories, Applied Supersymmetry and Quantum Gravity, Leuven, 10-14 July
'9

### Lifshitz quasinormal modes and relaxation from holography

We obtain relaxation times for field theories with Lifshitz scaling and with
holographic duals Einstein-Maxwell-Dilaton gravity theories. This is done by
computing quasinormal modes of a bulk scalar field in the presence of Lifshitz
black branes. We determine the relation between relaxation time and dynamical
exponent z, for various values of boundary dimension d and operator scaling
dimension. It is found that for d>z+1, at zero momenta, the modes are
non-overdamped, whereas for d<=z+1 the system is always overdamped. For d=z+1
and zero momenta, we present analytical results.Comment: 16 pages and 5 figure

### Static supersymmetric black holes in AdS_4 with spherical symmetry

We elaborate further on the static supersymmetric AdS_4 black holes found in
arXiv:0911.4926, investigating thoroughly the BPS constraints for spherical
symmetry in N = 2 gauged supergravity in the presence of Fayet-Iliopoulos
terms. We find Killing spinors that preserve two of the original eight
supercharges and investigate the conditions for genuine black holes free of
naked singularities. The existence of a horizon is intimately related with the
requirement that the scalars are not constant, but given in terms of harmonic
functions in analogy to the attractor flow in ungauged supergravity. The black
hole charges depend on the choice of the electromagnetic gauging, with only
magnetic charges for purely electric gaugings. Finally we show how these black
holes can be embedded in N = 8 supergravity and thus in M-theory.Comment: 28 pages; v2 minor change

### Lifshitz entanglement entropy from holographic cMERA

We study entanglement entropy in free Lifshitz scalar field theories
holographically by employing the metrics proposed by Nozaki, Ryu and Takayanagi
in \cite{Nozaki:2012zj} obtained from a continuous multi-scale entanglement
renormalisation ansatz (cMERA). In these geometries we compute the minimal
surface areas governing the entanglement entropy as functions of the dynamical
exponent $z$ and we exhibit a transition from an area law to a volume law
analytically in the limit of large $z$. We move on to explore the effects of a
massive deformation, obtaining results for any $z$ in arbitrary dimension. We
then trigger a renormalisation group flow between a Lifshitz theory and a
conformal theory and observe a monotonic decrease in entanglement entropy along
this flow. We focus on strip regions but also consider a disc in the undeformed
theory.Comment: 17 pages, v2: references added and improved discussions, v3:
published versio

### Phase transitions of magnetic AdS4 black holes with scalar hair

We determine the thermodynamic properties of a class of spherically symmetric
and static black holes in AdS4 with magnetic charges and scalar hair. These
black holes are solutions in 4d N=2 gauged supergravity that can arise from
eleven-dimensional supergravity compactified on S^7. At zero temperature, they
preserve supersymmetry and hence are stable. At non-zero temperatures, we
explore in detail the canonical ensemble and stability of solutions and find a
first order phase transition between small and large hairy black holes. The
transition emerges as a liquid-gas phase transition in the dual
three-dimensional field theory on R x S^2 with magnetic flux through S^2.Comment: 5 pages, v2: misprints corrected and references added, published
versio

### Fivebrane Instanton Corrections to the Universal Hypermultiplet

We analyze the Neveu-Schwarz fivebrane instanton in type IIA string theory
compactifications on rigid Calabi-Yau threefolds, in the low-energy
supergravity approximation. It there appears as a finite action solution to the
Euclidean equations of motion of a double-tensor multiplet (dual to the
universal hypermultiplet) coupled to N=2, D=4 supergravity. We determine the
bosonic and fermionic zero modes, and the single-centered instanton measure on
the moduli space of collective coordinates. The results are then used to
compute, in the semiclassical approximation, correlation functions that
nonperturbatively correct the universal hypermultiplet moduli space geometry of
the low-energy effective action. We find that only the Ramond-Ramond sector
receives corrections, and we discuss the breaking of isometries due to
instantons.Comment: 48 pages, v2: improved version with some correction

### Hyperkahler Cones and Orthogonal Wolf Spaces

We construct the hyperkahler cones corresponding to the Quaternion-Kahler
orthogonal Wolf spaces SO(n+4)/(SO(n)xSO(4)) and their non-compact versions,
which appear in hypermultiplet couplings to N=2 supergravity. The geometry is
completely encoded by a single function, the hyperkahler potential, which we
compute from an SU(2) hyperkahler quotient of flat space. We derive the Killing
vectors and moment maps for the SO(n+4) isometry group on the hyperkahler cone.
For the non-compact case, the isometry group SO(n,4) contains n+2 abelian
isometries which can be used to find a dual description in terms of n tensor
multiplets and one double-tensor multiplet. Finally, using a representation of
the hyperkahler quotient via quiver diagrams, we deduce the existence of a new
eight dimensional ALE space.Comment: 19 pages, Latex, 2 figures (references added

### A 5d/2d/4d correspondence

We propose a correspondence between two-dimensional (0,4) sigma models with
target space the moduli spaces of r monopoles, and four-dimensional N=4, U(r)
Yang-Mills theory on del Pezzo surfaces. In particular, the two- and
four-dimensional BPS partition functions are argued to be equal. The
correspondence relies on insights from five-dimensional supersymmetric gauge
theory and its geometric engineering in M-theory, hence the name "5d/2d/4d
correspondence". We provide various tests of our proposal. The most stringent
ones are for r=1, for which we prove the equality of partition functions.Comment: 39 pages, final versio

### Entanglement Entropy in Lifshitz Theories

We discuss and compute entanglement entropy (EE) in (1+1)-dimensional free
Lifshitz scalar field theories with arbitrary dynamical exponents. We consider
both the subinterval and periodic sublattices in the discretized theory as
subsystems. In both cases, we are able to analytically demonstrate that the EE
grows linearly as a function of the dynamical exponent. Furthermore, for the
subinterval case, we determine that as the dynamical exponent increases, there
is a crossover from an area law to a volume law. Lastly, we deform Lifshitz
field theories with certain relevant operators and show that the EE decreases
from the ultraviolet to the infrared fixed point, giving evidence for a
possible c-theorem for deformed Lifshitz theories.Comment: 24 pages, 8 figures; v2: Clarified discussions in Subsection 3.3 and
appendix; v3: Major extension of results, including an analytic computation
of subinterval entanglement in massless scalar Lifshitz theories; v4: Added
footnote 4 for clarification, version to appear in SciPos

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