Supersymmetric Lifshitz-like backgrounds from N=4 SYM with heavy quark density

We examine a class of gravity backgrounds obtained by considering the backreaction of a spatially uniform density of mutually BPS Wilson lines or heavy quarks in N=4 SUSY Yang-Mills theory. The configurations preserve eight supercharges and an SO(5) subgroup of the SO(6) R-symmetry. They are obtained by considering the 1/4-BPS geometries associated to smeared string/D3-brane (F1-D3) intersections. We argue that for the (partially) localized intersection, the geometry exhibits a flow from AdS_5 x S^5 in the UV to a novel IR scaling solution displaying anisotropic Lifshitz-like scaling with dynamical critical exponent z=7, hyperscaling violation and a logarithmic running dilaton. We also obtain a two-parameter family of smeared 1/4-BPS solutions on the Coulomb branch of N=4 SYM exhibiting Lifshitz scaling and hyperscaling violation. For a certain parametric range these yield IR geometries which are conformal to AdS_2 x R^3, and which have been argued to be relevant for fermionic physics.Comment: 24 pages, 2 figures, references added, version published in JHEP, Feb. 201

Unimodular cosmology and the weight of energy

Some models are presented in which the strength of the gravitational coupling of the potential energy relative to the same coupling for the kinetic energy is, in a precise sense, adjustable. The gauge symmetry of these models consists of those coordinate changes with unit jacobian.Comment: LaTeX, 23 pages, conclusions expanded. Two paragraphs and a new reference adde

One-loop effective potential in M4 x T2 with and without 't Hooft flux

We review the basic notions of compactification in the presence of a background flux. In extra-dimentional models with more than five dimensions, Scherk and Schwarz boundary conditions have to satisfy 't Hooft consistency conditions. Different vacuum configurations can be obtained, depending whether trivial or non-trivial 't Hooft flux is considered. The presence of the "magnetic" background flux provide, in addition, a mechanism for producing four-dimensional chiral fermions. Particularizing to the six-dimensional case, we calculate the one-loop effective potential for a U(N) gauge theory on M4 x T2. We firstly review the well known results of the trivial 't Hooft flux case, where one-loop contributions produce the usual Hosotani dynamical symmetry breaking. Finally we applied our result for describing, for the first time, the one-loop contributions in the non-trivial 't Hooft flux case

Data-based control synthesis and performance assessment for moored wave energy conversion systems: the PeWEC case

With a model-based control strategy, the effectiveness of the associated control action depends on the availability of a representative control-oriented model. In the case of floating offshore wave energy converters (WECs), the device response depends upon the interaction between mooring system, any mechanical parts, and the hydrodynamics of the floating body. This study proposes an approach to synthesise WEC controllers under the effect of mooring forces building a representative data-based linear model able to include any relevant dynamics. Moreover, the procedure is tested on the moored pendulum wave energy converter (PeWEC) by means of a high-fidelity mooring solver, OrcaFlex (OF). In particular, the control action is computed with and without knowledge of the mooring influence, in order to analyse and elucidate the effect of the station-keeping system on the harvested energy. The performance assessment of the device is achieved by evaluating device power on the resource scatter characterising Pantelleria, Italy. The results show the relevance of the mooring dynamics on the device response and final set of control parameters and, hence, a significant influence of the station-keeping system on control synthesis and extracted mechanical power

Existence theorems for lagrange control problems with unbounded time domain

Existence theorems are proved for usual Lagrange control systems, in which the time domain is unbounded. As usual in Lagrange problems, the cost functional is an improper integral, the state equation is a system of ordinary differential equations, with assigned boundary conditions, and constraints may be imposed on the values of the state and control variables. It is shown that the boundary conditions at infinity require a particular analysis. Problems of this form can be found in econometrics (e.g., infinite-horizon economic models) and operations research (e.g., search problems).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45207/1/10957_2004_Article_BF00934054.pd

Quantum corrections to Higher-Dimensional Theories

This is a non-technical summary of the subtleties of quantum corrections on extra-dimensional theories: should one first renormalize and then mode expand, or first expand in four-dimensional modes and then renormalize?Comment: 9 pages, based on a talk at IRGAC 2006, Barcelon