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 $10^{14}$ in the standard cold inflationary scenario.Comment: 9 pages, RevTe

Quantizing higher-spin gravity in free-field variables

We study the formulation of massless higher-spin gravity on AdS$_3$ 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 $W_N$ CFT's: the generators of the residual gauge symmetries are the classical limits of screening charges, while the gauge-invariant observables are classical $W_N$ charges. Quantization in these variables can be carried out using standard techniques and makes manifest a remnant of the triality symmetry of $W_\infty[\lambda]$. 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 $W_N$ primaries, to all orders in the large central charge expansion.Comment: 31 pages + appendices. V2: typos corrected, reference adde

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 $H^2 \sim \rho^q$ in the asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to $q=2$ whereas $q=2/3$ & $q=1$ 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 $V(\phi) \sim \phi^p$ investigated in this paper, the scalar to tensor ratio of perturbations $R$ is maximum around the RS region and is generally suppressed in the high energy regime for the positive values of $p$. The ratio is very low for $p>0$ 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 $p$ turn out to be in the $1 \sigma$ observational contour bound at all energy scales varying from GR to high energy GB limit. The spectral index $n_S$ improves for the lower values of $p$ and approaches its scale invariant limit for $p=-2$ in the high energy GB regime. The ratio $R$ also remains small for large negative values of $p$, 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 $H^2 \sim \rho^q$, the behavior of ordinary scalar field near cosmological singularity and the nature of scaling solutions are distinguished for the values of $q 1$.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

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

Conical Defects in Higher Spin Theories

We study conical defect geometries in the SL(N) Chern-Simons formulation of higher spin gauge theories in AdS_3. We argue that (for N\geq 4) there are special values of the deficit angle for which these geometries are actually smooth configurations of the underlying theory. We also exhibit a gauge in which these geometries can be viewed as wormholes interpolating between two distinct asymptotically AdS_3 spacetimes. Remarkably, the spectrum of smooth SL(N,C) solutions, after an appropriate analytic continuation, exactly matches that of the so-called "light primaries" in the minimal model W_N CFTs at finite N. This gives a candidate bulk interpretation of the latter states in the holographic duality proposed in [1].Comment: 38 page

Off-Shell Interactions for Closed-String Tachyons

Off-shell interactions for localized closed-string tachyons in C/Z_N superstring backgrounds are analyzed and a conjecture for the effective height of the tachyon potential is elaborated. At large N, some of the relevant tachyons are nearly massless and their interactions can be deduced from the S-matrix. The cubic interactions between these tachyons and the massless fields are computed in a closed form using orbifold CFT techniques. The cubic interaction between nearly-massless tachyons with different charges is shown to vanish and thus condensation of one tachyon does not source the others. It is shown that to leading order in N, the quartic contact interaction vanishes and the massless exchanges completely account for the four point scattering amplitude. This indicates that it is necessary to go beyond quartic interactions or to include other fields to test the conjecture for the height of the tachyon potential.Comment: 37 pages, 3 figures, LaTeX, JHEP class. Typos corrected, references added, published versio

Comments on D-brane Interactions in PP-wave Backgrounds

We calculate the interaction potential between widely separated D-branes in PP-wave backgrounds in string theory as well as in low-energy supergravity. Timelike and spacelike orientations are qualitatively different but in both cases the effective brane tensions and RR charges take the same values as in Minkowski space in accordance with the expectations from the sigma model perturbation theory.Comment: Latex, 22 pages. Typos corrected and a reference added, final versio