Absorption on horizon-wrapped branes

We compute the absorption cross section of space-time scalars on a static D2 rane, in global coordinates, wrapped on the S^2 of an AdS_2 X S^2 X CY_3 geometry. We discuss its relevance for the construction of the dual quantum mechanics of Calabi-Yau black holes.Comment: 18 pages, 2 figure

Non-equilibrium Dynamics of O(N) Nonlinear Sigma models: a Large-N approach

We study the time evolution of the mass gap of the O(N) non-linear sigma model in 2+1 dimensions due to a time-dependent coupling in the large-$N$ limit. Using the Schwinger-Keldysh approach, we derive a set of equations at large $N$ which determine the time dependent gap in terms of the coupling. These equations lead to a criterion for the breakdown of adiabaticity for slow variation of the coupling leading to a Kibble-Zurek scaling law. We describe a self-consistent numerical procedure to solve these large-$N$ equations and provide explicit numerical solutions for a coupling which starts deep in the gapped phase at early times and approaches the zero temperature equilibrium critical point $g_c$ in a linear fashion. We demonstrate that for such a protocol there is a value of the coupling $g= g_c^{\rm dyn}> g_c$ where the gap function vanishes, possibly indicating a dynamical instability. We study the dependence of $g_c^{\rm dyn}$ on both the rate of change of the coupling and the initial temperature. We also verify, by studying the evolution of the mass gap subsequent to a sudden change in $g$, that the model does not display thermalization within a finite time interval $t_0$ and discuss the implications of this observation for its conjectured gravitational dual as a higher spin theory in $AdS_4$.Comment: 22 pages, 9 figures. Typos corrected, references rearranged and added.v3 : sections rearranged, abstract modified, comment about Kibble-Zurek scaling correcte

Possible Hypoxia Signaling Induced Alteration of Glucose Homeostasis in Rats Exposed to Chronic Intermittent Hypoxia - Role of Antioxidant (Vitamin C) and Ca2+ Channel Blocker (Cilnidipine)

Background: Hyperglycemia is found to be a regulator of HIF-1α gene expression but the regulation of HIF-1α on glucose homeostasis is unclear. Objective: To determine whether chronic intermittent hypoxia (CIH) alters glucose regulation and such alterations can revert through treatments with either antioxidant (vitamin c) or calcium channel blocker (cilnidipine) in male albino rats. Methods: The rats were divided into six groups i.e. normoxia (21% oxygen), CIH (10% oxygen with cycle time 3:1.5; 8h/day), normoxia with vitamin c (50 mg /100g. b.wt, orally), CIH with vitamin c, normoxia with cilnidipine (1 mg/kg/day; ip) and CIH with cilnidipine. Serum MDA, HIF-1α, fasting plasma glucose, insulin, GTT, HOMA-IR and insulinogenic index were evaluated. Results: Serum HIF-1α and MDA concentration in rats exposed to CIH increased significantly whereas simultaneous CIH with vitamin c and CIH with cilnidipine treatment show reversion of both serum HIF- 1α and MDA concentrations towards normoxic status. CIH rats showed increased fasting glucose level with unchanged plasma insulin level but both vitamin c and cilnidipine treatment improved the status. Elevated HOMA-IR and insulinogenic index along with impaired GTT were found in CIH groups although vitamin c and cilnidipine improved the glucose homeostasis in CIH exposed rats. Conclusion: CIH induces over production of reactive oxygen species as well as hyper activities of sympathetic N-type Ca2+ channels possibly through HIF 1-α expression and influence on insulin signaling by causing hyperglycemia, glucose intolerance and insulin resistance in rats. Simultaneous treatment with vitamin c or cilnidipine improves glucose homeostasis in CIH exposed rats

Bi-local Construction of Sp(2N)/dS Higher Spin Correspondence

We derive a collective field theory of the singlet sector of the Sp(2N) sigma model. Interestingly the hamiltonian for the bilocal collective field is the same as that of the O(N) model. However, the large-N saddle points of the two models differ by a sign. This leads to a fluctuation hamiltonian with a negative quadratic term and alternating signs in the nonlinear terms which correctly reproduces the correlation functions of the singlet sector. Assuming the validity of the connection between O(N) collective fields and higher spin fields in AdS, we argue that a natural interpretation of this theory is by a double analytic continuation, leading to the dS/CFT correspondence proposed by Anninos, Hartman and Strominger. The bi-local construction gives a map into the bulk of de Sitter space-time. Its geometric pseudospin-representation provides a framework for quantization and definition of the Hilbert space. We argue that this is consistent with finite N grassmanian constraints, establishing the bi-local representation as a nonperturbative framework for quantization of Higher Spin Gravity in de Sitter space.Comment: 1 figur

Absorption of scalars by nonextremal charged black holes in string theory

We analyze the low frequency absorption cross section of minimally coupled massless scalar fields by different kinds of charged static black holes in string theory, namely the D1–D5 system in d=5 and a four dimensional dyonic four-charged black hole. In each case we show that this cross section always has the form of some parameter of the solution divided by the black hole Hawking temperature. We also verify in each case that, despite its explicit temperature dependence, such quotient is finite in the extremal limit, giving a well defined cross section. We show that this precise explicit temperature dependence also arises in the same cross section for black holes with string \alpha' corrections: it is actually induced by them.This work has been supported by FEDER funds through Programa Operacional Fatores de Competitividade – COMPETE and by Fundação para a Ciência e a Tecnologia (FCT) through projects EstC/MAT/UI0013/2011 and CERN/FP/123609/2011

Meson Thermalization in Various Dimensions

In gauge/gravity duality framework the thermalization of mesons in strongly coupled (p+1)-dimensional gauge theories is studied for a general Dp-Dq system, q>=p, using the flavour Dq-brane as a probe. Thermalization corresponds to the horizon formation on the flavour Dq-brane. We calculate the thermalization time-scale due to a time-dependent change in the baryon number chemical potential, baryon injection in the field theory. We observe that for such a general system it has a universal behaviour depending only on the t'Hooft coupling constant and the two parameters which describe how we inject baryons into the system. We show that this universal behaviour is independent of the details of the theory whether it is conformal and/or supersymmetric.Comment: 26 pages, 2 figure

Semantic Sentiment Analysis of Twitter Data

Internet and the proliferation of smart mobile devices have changed the way information is created, shared, and spreads, e.g., microblogs such as Twitter, weblogs such as LiveJournal, social networks such as Facebook, and instant messengers such as Skype and WhatsApp are now commonly used to share thoughts and opinions about anything in the surrounding world. This has resulted in the proliferation of social media content, thus creating new opportunities to study public opinion at a scale that was never possible before. Naturally, this abundance of data has quickly attracted business and research interest from various fields including marketing, political science, and social studies, among many others, which are interested in questions like these: Do people like the new Apple Watch? Do Americans support ObamaCare? How do Scottish feel about the Brexit? Answering these questions requires studying the sentiment of opinions people express in social media, which has given rise to the fast growth of the field of sentiment analysis in social media, with Twitter being especially popular for research due to its scale, representativeness, variety of topics discussed, as well as ease of public access to its messages. Here we present an overview of work on sentiment analysis on Twitter.Comment: Microblog sentiment analysis; Twitter opinion mining; In the Encyclopedia on Social Network Analysis and Mining (ESNAM), Second edition. 201

Intersecting black branes in strong gravitational waves

We consider intersecting black branes with strong gravitational waves propagating along their worldvolume in the context of supergravity theories. Both near-horizon and space-filling gravitational wave modes are included in our ansatz. The equations of motion (originally, partial differential equations) are shown to reduce to ordinary differential equations, which include a Toda-like system. For special arrangements of intersecting black branes, the Toda-like system becomes integrable, permitting a more thorough analysis of the gravitational equations of motion.Comment: 17 pages; v2: cosmetic improvements, published versio

Universal time-dependent deformations of Schrodinger geometry

We investigate universal time-dependent exact deformations of Schrodinger geometry. We present 1) scale invariant but non-conformal deformation, 2) non-conformal but scale invariant deformation, and 3) both scale and conformal invariant deformation. All these solutions are universal in the sense that we could embed them in any supergravity constructions of the Schrodinger invariant geometry. We give a field theory interpretation of our time-dependent solutions. In particular, we argue that any time-dependent chemical potential can be treated exactly in our gravity dual approach.Comment: 24 pages, v2: references adde

Stringy effects in black hole decay

We compute the low energy decay rates of near-extremal three(four) charge black holes in five(four) dimensional N=4 string theory to sub-leading order in the large charge approximation. This involves studying stringy corrections to scattering amplitudes of a scalar field off a black hole. We adapt and use recently developed techniques to compute such amplitudes as near-horizon quantities. We then compare this with the corresponding calculation in the microscopic configuration carrying the same charges as the black hole. We find perfect agreement between the microscopic and macroscopic calculations; in the cases we study, the zero energy limit of the scattering cross section is equal to four times the Wald entropy of the black hole.Comment: 32 page