An analytic Lifshitz black hole

A Lifshitz point is described by a quantum field theory with anisotropic scale invariance (but not Galilean invariance). In arXiv:0808.1725, gravity duals were conjectured for such theories. We construct analytically a black hole which asymptotes to a vacuum Lifshitz solution; this black hole solves the equations of motion of some simple (but somewhat strange) extensions of the models of arXiv:0808.1725. We study its thermodynamics and scalar response functions. The scalar wave equation turns out to be exactly solvable. Interestingly, the Green's functions do not exhibit the ultralocal behavior seen previously in the free Lifshitz scalar theory.Comment: 18 page

Perception Framework for Activities of Daily Living Manipulation Tasks

There is an increasing concern in tackling the problems faced by the elderly community and physically in-locked people to lead an independent life experience problems with self- care. The need for developing service robots that can help people with mobility impairments is hence very essential. Developing a control framework for shared human-robot autonomy will allow locked-in individuals to perform the Activities of Daily Living (ADL) in a exible way. The relevant ADL scenarios were identi ed as handling objects, self-feeding, and opening doors for indoor nav- igation assistance. Multiple experiments were conducted, which demonstrates that the robot executes these daily living tasks reliably without requiring adjustment to the environment. The indoor manipulation tasks hold the challenge of dealing with a wide range of unknown objects. This thesis presents a framework developed for grasping without requiring a priori knowledge of the objects being manipulated. A successful manipulation task requires the combination of aspects such as envi- ronment modeling, object detection with pose estimation, grasp planning, motion planning followed by an e?cient grasp execution, which is validated by a 6+2 Degree of Freedom robotic manipulator

Inclusion control in steel castings

“Non-metallic inclusions are mainly comprised of oxides, sulfides, and nitrides, and are formed in liquid steel during the melting and refining process, as a result of reoxidation, worn-out refractories, or entrained slag. The notch toughness of high strength steels is particularly susceptible to the type, number, size, and distribution of non-metallic inclusions. High manganese and aluminum austenitic steels, or Fe-Mn-Al steels, have gained much interest in the military and automotive sector because of their excellent combinations of high strength and toughness. However, these steels are subject to both oxide bifilms and aluminum nitride, AlN, inclusions which form during melting and casting. During the casting process, the gating system plays an important role in determining the casting quality and the overall level of inclusions and bifilm defects. Two solutions to control inclusions during mold filling include molten metal filtration and design of novel “naturally pressurized” gating systems that control metal flow into the casting cavity and reduce air entrainment. However, the use of filters and these naturally pressurized gating systems add an additional cost and generally reduce casting yield. In the current study, the effects of filtration and gating design on reduction of bifilms and inclusions in Fe-Mn-Al steel were determined using two novel mold designs. A parallel gating study involving an aluminum deoxidized, cast composition of SAE 8630 was also performed. The results of this study showed that ceramic foam filters were more effective at removing solid oxide bifilms and aluminum nitride inclusions from Fe-Mn-Al steel castings than the naturally pressurized gating systems. Future studies should be directed at developing naturally pressurized gating systems with filters”--Abstract, page iv

Holographic view of non-relativistic physics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 167-177).Motivated by the AdS/CFT correspondence for relativistic CFTs, it seems natural to generalize it to non-relativistic CFTs. Such a dual description could provide insight into strong coupling phenomena observed in condensed matter systems. Scale invariance can be realized in non-relativistic theories in many ways. One freedom is the relative scale dimension of time and space, called the dynamical exponent z. In this thesis, we will mainly focus on the case where z = 2, however gravity duals for other values of z have also been found. In the first part of the thesis, we study NRCFTs that are Galilean invariant. Discrete light cone quantization (DLCQ) of V= 4 super Yang-Mills theory is an example of such a system with z = 2 scaling symmetry. A more realistic example of a system with the same set of symmetries is a system of cold fermions at unitarity. These non-relativistic systems respect a symmetry algebra known as the Schrödinger algebra. We propose a gravity dual that realizes the symmetries of the Schrödinger algebra as isometries. An unusual feature of this duality is that the bulk geometry has two extra dimensions than the CFT, instead of the usual one. The additional direction is a compact direction and shift symmetry along this direction corresponds to the particle number transformation. This solution can be embedded into string theory by performing a set of operations (known as the Null-Melvin twist) on AdS5 x S' solution of type IIB supergravity. This method also provides a way of finding a black hole solution which has asymptotic Schrödinger symmetries. The field theory dual of these gravity solutions happens to be a modified version of DLCQ V = 4 super Yang-Mills theory. The thermodynamics of these theories is very different from that of cold atoms. This happens to be a consequence of realizing the entire Schrödinger group as isometries of the spacetime. We give an example of a holographic realization in which the particle number symmetry is realized as a bulk gauge symmetry. In this proposal, the Schrödinger algebra is realized in the bulk without the introduction of an additional compact direction. Using this proposal, we find a confining solution that describes a non-relativistic system at finite density. We use the holographic dictionary to compute the conductivity of this system and it is found to exhibit somewhat unusual behavior. In the second part of the thesis we study gravity duals of Lifshitz theories. These are non-relativistic scale invariant theories that are not boost invariant. These theories do not have a particle number symmetry unlike the boost invariant NRCFTs. We present solutions of 1OD and 111D supergravity theories that are dual to Lifshitz theories. We present a black hole solution that is dual to a strongly interacting Lifshitz theory at finite temperature. We show that the finite temperature correlators in the interacting theories do not exhibit ultra-local behavior which was observed in free Lifshitz theories.by Koushik Balasubramanian.Ph.D

Hot Spacetimes for Cold Atoms

Building on our earlier work and that of Son, we construct string theory duals of non-relativistic critical phenomena at finite temperature and density. Concretely, we find black hole solutions of type IIB supergravity whose asymptotic geometries realize the Schroedinger group as isometries. We then identify the non-relativistic conformal field theories to which they are dual. We analyze the thermodynamics of these black holes, which turn out to describe the system at finite temperature and finite density. The strong-coupling result for the shear viscosity of the dual non-relativistic field theory saturates the KSS bound.Comment: latex, 40+1 pages; v2: added subsection 4.6, solidified calculation of stress tensor, added ref

Gravity duals for non-relativistic CFTs

We attempt to generalize the AdS/CFT correspondence to non-relativistic conformal field theories which are invariant under Galilean transformations. Such systems govern ultracold atoms at unitarity, nucleon scattering in some channels, and more generally, a family of universality classes of quantum critical behavior. We construct a family of metrics which realize these symmetries as isometries. They are solutions of gravity with negative cosmological constant coupled to pressureless dust. We discuss realizations of the dust, which include a bulk superconductor. We develop the holographic dictionary and compute some two-point correlators. A strange aspect of the correspondence is that the bulk geometry has two extra noncompact dimensions.Comment: 12 pages; v2, v3, v4: added references, minor corrections; v3: cleaned up and generalized dust; v4: closer to published versio

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