386 research outputs found
Warm tachyonic inflation in warped background
We analyze warm tachyonic inflation, proposed in the literature, but from the
viewpoint of four dimensional effective action for tachyon field on a non-BPS
D3-brane. We find that consistency with observational data on density
perturbation and validity of effective action requires warped compactification.
The number of background branes which source the flux is found to be of the
order of 10 in contrast to the order of in the standard cold
inflationary scenario.Comment: 9 pages, RevTe
Parasite escape through trophic specialization in a species flock
Submitted version (preprint).submittedVersio
Adaptive divergence under gene flow along an environmental gradient in two coexisting stickleback species
publishedVersio
Quantizing higher-spin gravity in free-field variables
We study the formulation of massless higher-spin gravity on AdS in a
gauge in which the fundamental variables satisfy free field Poisson brackets.
This gauge choice leaves a small portion of the gauge freedom unfixed, which
should be further quotiented out. We show that doing so leads to a bulk version
of the Coulomb gas formalism for CFT's: the generators of the residual
gauge symmetries are the classical limits of screening charges, while the
gauge-invariant observables are classical charges. Quantization in these
variables can be carried out using standard techniques and makes manifest a
remnant of the triality symmetry of . This symmetry can be
used to argue that the theory should be supplemented with additional matter
content which is precisely that of the Prokushkin-Vasiliev theory. As a further
application, we use our formulation to quantize a class of conical surplus
solutions and confirm the conjecture that these are dual to specific degenerate
primaries, to all orders in the large central charge expansion.Comment: 31 pages + appendices. V2: typos corrected, reference adde
Black Hole Meiosis
The enumeration of BPS bound states in string theory needs refinement.
Studying partition functions of particles made from D-branes wrapped on
algebraic Calabi-Yau 3-folds, and classifying states using split attractor flow
trees, we extend the method for computing a refined BPS index, arXiv:0810.4301.
For certain D-particles, a finite number of microstates, namely polar states,
exclusively realized as bound states, determine an entire partition function
(elliptic genus). This underlines their crucial importance: one might call them
the `chromosomes' of a D-particle or a black hole. As polar states also can be
affected by our refinement, previous predictions on elliptic genera are
modified. This can be metaphorically interpreted as `crossing-over in the
meiosis of a D-particle'. Our results improve on hep-th/0702012, provide
non-trivial evidence for a strong split attractor flow tree conjecture, and
thus suggest that we indeed exhaust the BPS spectrum. In the D-brane
description of a bound state, the necessity for refinement results from the
fact that tachyonic strings split up constituent states into `generic' and
`special' states. These are enumerated separately by topological invariants,
which turn out to be partitions of Donaldson-Thomas invariants. As modular
predictions provide a check on many of our results, we have compelling evidence
that our computations are correct.Comment: 46 pages, 8 figures. v2: minor changes. v3: minor changes and
reference adde
String theory duals of Lifshitz-Chern-Simons gauge theories
We propose candidate gravity duals for a class of non-Abelian z=2 Lifshitz
Chern-Simons (LCS) gauge theories studied by Mulligan, Kachru and Nayak. These
are nonrelativistic gauge theories in 2+1 dimensions in which parity and
time-reversal symmetries are explicitly broken by the presence of a
Chern-Simons term. We show that these field theories can be realized as
deformations of DLCQ N=4 super Yang-Mills theory. Using the holographic
dictionary, we identify the bulk fields that are dual to these deformations.
The geometries describing the groundstates of the non-Abelian LCS gauge
theories realized here exhibit a mass gap.Comment: 25+14 pages, 3 figures; v2: significant corrections regarding IR
geometry, resulting in new section 5; journal versio
Harmonic Analysis of Boolean Networks: Determinative Power and Perturbations
Consider a large Boolean network with a feed forward structure. Given a
probability distribution on the inputs, can one find, possibly small,
collections of input nodes that determine the states of most other nodes in the
network? To answer this question, a notion that quantifies the determinative
power of an input over the states of the nodes in the network is needed. We
argue that the mutual information (MI) between a given subset of the inputs X =
{X_1, ..., X_n} of some node i and its associated function f_i(X) quantifies
the determinative power of this set of inputs over node i. We compare the
determinative power of a set of inputs to the sensitivity to perturbations to
these inputs, and find that, maybe surprisingly, an input that has large
sensitivity to perturbations does not necessarily have large determinative
power. However, for unate functions, which play an important role in genetic
regulatory networks, we find a direct relation between MI and sensitivity to
perturbations. As an application of our results, we analyze the large-scale
regulatory network of Escherichia coli. We identify the most determinative
nodes and show that a small subset of those reduces the overall uncertainty of
the network state significantly. Furthermore, the network is found to be
tolerant to perturbations of its inputs
Tachyon Vacuum in Cubic Superstring Field Theory
In this paper we give an exact analytic solution for tachyon condensation in
the modified (picture 0) cubic superstring field theory. We prove the absence
of cohomology and, crucially, reproduce the correct value for the D-brane
tension. The solution is surprising for two reasons: First, the existence of a
tachyon vacuum in this theory has not been definitively established in the
level expansion. Second, the solution {\it vanishes} in the GSO sector,
implying a ``tachyon vacuum'' solution exists even for a {\it BPS} D-brane.Comment: 16 pages, 2 figure
Aspects of Scalar Field Dynamics in Gauss-Bonnet Brane Worlds
The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to
a complicated Friedmann equation which simplifies to in the
asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to
whereas & give rise to high energy Gauss-Bonnet (GB) regime and
the standard GR respectively. Amazingly, while evolving from RS regime to high
energy GB limit, one passes through a GR like region which has important
implications for brane world inflation. For tachyon GB inflation with
potentials investigated in this paper, the scalar to
tensor ratio of perturbations is maximum around the RS region and is
generally suppressed in the high energy regime for the positive values of .
The ratio is very low for at all energy scales relative to GB inflation
with ordinary scalar field. The models based upon tachyon inflation with
polynomial type of potentials with generic positive values of turn out to
be in the observational contour bound at all energy scales varying
from GR to high energy GB limit. The spectral index improves for the
lower values of and approaches its scale invariant limit for in the
high energy GB regime. The ratio also remains small for large negative
values of , however, difference arises for models close to scale invariance
limit. In this case, the tensor to scale ratio is large in the GB regime
whereas it is suppressed in the intermediate region between RS and GB. Within
the frame work of patch cosmologies governed by , the behavior
of ordinary scalar field near cosmological singularity and the nature of
scaling solutions are distinguished for the values of .Comment: 15 pages, 10 eps figures; appendix on various scales in GB brane
world included and references updated; final version to appear in PR
At the horizon of a supersymmetric AdS_5 black hole: Isometries and half-BPS giants
The near-horizon geometry of an asymptotically AdS_5 supersymmetric black
hole discovered by Gutowski and Reall is analysed. After lifting the solution
to 10 dimensions, we explicitly solve the Killing spinor equations in both
Poincare and global coordinates. It is found that exactly four supersymmetries
are preserved which is twice the number for the full black hole. The full set
of isometries is constructed and the isometry supergroup is shown to be
SU(1,1|1) X SU(2) X U(3). We further study half-BPS configurations of D3-branes
in the near-horizon geometry in Poincare and global coordinates. Both giant
graviton probes and dual giant graviton probes are found.Comment: 26 pages. v2:Typos corrected, minor change
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