67 research outputs found
Massless particles on supergroups and AdS3 x S3 supergravity
Firstly, we study the state space of a massless particle on a supergroup with
a reparameterization invariant action. After gauge fixing the
reparameterization invariance, we compute the physical state space through the
BRST cohomology and show that the quadratic Casimir Hamiltonian becomes
diagonalizable in cohomology. We illustrate the general mechanism in detail in
the example of a supergroup target GL(1|1). The space of physical states
remains an indecomposable infinite dimensional representation of the space-time
supersymmetry algebra. Secondly, we show how the full string BRST cohomology in
the particle limit of string theory on AdS3 x S3 renders the quadratic Casimir
diagonalizable, and reduces the Hilbert space to finite dimensional
representations of the space-time supersymmetry algebra (after analytic
continuation). Our analysis provides an efficient way to calculate the
Kaluza-Klein spectrum for supergravity on AdS3 x S3. It may also be a step
towards the identification of an interesting and simpler subsector of
logarithmic supergroup conformal field theories, relevant to string theory.Comment: 16 pages, 10 figure
3D N=6 Gauged Supergravity: Admissible Gauge Groups, Vacua and RG Flows
We study N=6 gauged supergravity in three dimensions with scalar manifolds
for in great details. We
classify some admissible non-compact gauge groups which can be consistently
gauged and preserve all supersymmetries. We give the explicit form of the
embedding tensors for these gauge groups as well as study their scalar
potentials on the full scalar manifold for each value of along with
the corresponding vacua. Furthermore, the potentials for the compact gauge
groups, for ,
identified previously in the literature are partially studied on a submanifold
of the full scalar manifold. This submanifold is invariant under a certain
subgroup of the corresponding gauge group. We find a number of supersymmetric
AdS vacua in the case of compact gauge groups. We then consider holographic RG
flow solutions in the compact gauge groups and
for the k=4 case. The solutions
involving one active scalar can be found analytically and describe operator
flows driven by a relevant operator of dimension 3/2. For non-compact gauge
groups, we find all types of vacua namely AdS, Minkowski and dS, but there is
no possibility of RG flows in the AdS/CFT sense for all gauge groups considered
here.Comment: 43 pages, no figures references added, typoes corrected and more
information adde
Universality and exactness of Schrodinger geometries in string and M-theory
We propose an organizing principle for classifying and constructing
Schrodinger-invariant solutions within string theory and M-theory, based on the
idea that such solutions represent nonlinear completions of linearized vector
and graviton Kaluza-Klein excitations of AdS compactifications. A crucial
simplification, derived from the symmetry of AdS, is that the nonlinearities
appear only quadratically. Accordingly, every AdS vacuum admits infinite
families of Schrodinger deformations parameterized by the dynamical exponent z.
We exhibit the ease of finding these solutions by presenting three new
constructions: two from M5 branes, both wrapped and extended, and one from the
D1-D5 (and S-dual F1-NS5) system. From the boundary perspective, perturbing a
CFT by a null vector operator can lead to nonzero beta-functions for spin-2
operators; however, symmetry restricts them to be at most quadratic in
couplings. This point of view also allows us to easily prove nonrenormalization
theorems: for any Sch(z) solution of two-derivative supergravity constructed in
the above manner, z is uncorrected to all orders in higher derivative
corrections if the deforming KK mode lies in a short multiplet of an AdS
supergroup. Furthermore, we find infinite classes of 1/4 BPS solutions with
4-,5- and 7-dimensional Schrodinger symmetry that are exact.Comment: 31 pages, plus appendices; v2, minor corrections, added refs, slight
change in interpretation in section 2.3, new Schrodinger and Lifshitz
solutions included; v3, clarifications in sections 2 and 3 regarding
existence of solutions and multi-trace operator
Kerr/CFT, dipole theories and nonrelativistic CFTs
We study solutions of type IIB supergravity which are SL(2,R) x SU(2) x
U(1)^2 invariant deformations of AdS_3 x S^3 x K3 and take the form of products
of self-dual spacelike warped AdS_3 and a deformed three-sphere. One of these
backgrounds has been recently argued to be relevant for a derivation of
Kerr/CFT from string theory, whereas the remaining ones are holographic duals
of two-dimensional dipole theories and their S-duals. We show that each of
these backgrounds is holographically dual to a deformation of the DLCQ of the
D1-D5 CFT by a specific supersymmetric (1,2) operator, which we write down
explicitly in terms of twist operators at the free orbifold point. The
deforming operator is argued to be exactly marginal with respect to the
zero-dimensional nonrelativistic conformal (or Schroedinger) group - which is
simply SL(2,R)_L x U(1)_R. Moreover, in the supergravity limit of large N and
strong coupling, no other single-trace operators are turned on. We thus propose
that the field theory duals to the backgrounds of interest are nonrelativistic
CFTs defined by adding the single Schroedinger-invariant (1,2) operator
mentioned above to the original CFT action. Our analysis indicates that the
rotating extremal black holes we study are best thought of as finite
right-moving temperature (non-supersymmetric) states in the above-defined
supersymmetric nonrelativistic CFT and hints towards a more general connection
between Kerr/CFT and two-dimensional non-relativistic CFTs.Comment: 48+8 pages, 4 figures; minor corrections and references adde
Concurrence of form and function in developing networks and its role in synaptic pruning
A fundamental question in neuroscience is how structure and function of neural systems are
related. We study this interplay by combining a familiar auto-associative neural network with
an evolving mechanism for the birth and death of synapses. A feedback loop then arises
leading to two qualitatively different types of behaviour. In one, the network structure
becomes heterogeneous and dissasortative, and the system displays good memory performance;
furthermore, the structure is optimised for the particular memory patterns stored
during the process. In the other, the structure remains homogeneous and incapable of pattern
retrieval. These findings provide an inspiring picture of brain structure and dynamics that
is compatible with experimental results on early brain development, and may help to explain
synaptic pruning. Other evolving networks—such as those of protein interactions—might
share the basic ingredients for this feedback loop and other questions, and indeed many of
their structural features are as predicted by our model.We are grateful for financial support from the Spanish MINECO (project of Excellence:
FIS2017-84256-P) and from “Obra Social La Caixa”
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