On Geodesic Motion in Horava-Lifshitz Gravity

We propose an action for a free particle in Horava-Lifshitz gravity based on Foliation Preserving Diffeomorphisms. The action reduces to the usual relativistic action in the low energy limit and allows for subluminal and superluminal motions with upper and lower bounds on velocity respectively. We find that deviation from general relativity is governed by a position dependent coupling constant which also depends on the mass of the particle. As a result, light-like geodesics are not affected whereas massive particles follow geodesics that become mass dependent and hence the equivalence principle is violated. We make an exact study for geodesics in flat space and a qualitative analysis for those in a spherically symmetric curved background.Comment: 12 pages, Dedicated to Farhad Ardalan on his 70th birthda

Temperature in the Throat

We study the temperature of extended objects in string theory. Rotating probe D-branes admit horizons and temperatures a la Unruh effect. We find that the induced metrics on slow rotating probe D1-branes in holographic string solutions including warped Calabi-Yau throats have distinct thermal horizons with characteristic Hawking temperatures even if there is no black hole in the bulk Calabi-Yau. Taking the UV/IR limits of the solution, we show that the world volume black hole nucleation depends on the deformation and the warping of the throat. We find that world volume horizons and temperatures of expected features form not in the regular confining IR region but in the singular nonconfining UV solution. In the conformal limit of the UV, we find horizons and temperatures similar to those on rotating probes in the AdS throat found in the literature. In this case, we also find that activating a background gauge field form the U(1) R--symmetry modifies the induced metric with its temperature describing two different classes of black hole solutions.Comment: Revised, extended and published versio

Quantum Local Quench, AdS/BCFT and Yo-Yo String

We propose a holographic model for local quench in 1+1 dimensional Conformal Field Theory (CFT). The local quench is produced by joining two identical CFT's on semi-infinite lines. When these theories have a zero boundary entropy, we use the AdS/Boundary CFT proposal to describe this process in terms of bulk physics. Boundaries of the original CFT's are extended in AdS as dynamical surfaces. In our holographic picture these surfaces detach from the boundary and form a closed folded string which can propagate in the bulk. The dynamics of this string is governed by the tensionless Yo-Yo string solution and its subsequent evolution determines the time dependence after quench. We use this model to calculate holographic Entanglement Entropy (EE) of an interval as a function of time. We propose how the falling string deforms Ryu-Takayanagi's curves. Using the deformed curves we calculate EE and find complete agreement with field theory results.Comment: 20 pages, 13 figures, discussion improved, Version to appear in JHE

Dual Spikes; New Spiky String Solutions

We find a new class of spiky solutions for closed strings in flat, $AdS_3\subset AdS_5$ and $R\times S^2(\subset S^5)$ backgrounds. In the flat case the new solutions turn out to be T-dual configurations of spiky strings found by Kruczenski hep-th/0410226. In the case of solutions living in $AdS$, we make a semi classical analysis by taking the large angular momentum limit. The anomalous dimension for these dual spikes is similar to that for rotating and pulsating circular strings in AdS with angular momentum playing the role of the level number. This replaces the well known logarithmic dependence for spinning strings. For the dual spikes living on sphere we find that no large angular momentum limit exists.Comment: Added reference

Symmetric Orbifolds and Entanglement Entropy for Primary Excitations in Two Dimensional CFT

We use the techniques in symmetric orbifolding to calculate the Entanglement Entropy of a single interval in a two dimensional conformal field theory on a circle which is excited to a pure highest weight state. This is achieved by calculating the Reney Entropy which is found in terms of a 2n-point function of primary operators, n being the replica number