224 research outputs found
Long distance modifications of gravity in four dimensions
We discuss some general characteristics of modifications of the 4D
Einstein-Hilbert action that become important for low space-time curvatures. In
particular we focus on the chameleon-like behaviour of the massive
gravitational degrees of freedom. Generically there is at least one extra
scalar that is light on cosmic scales, but for certain models it becomes heavy
close to any mass source.Comment: 4 pages, contribution to the proceedings of the Rencontres de
Moriond: Contents and Structures of the Universe, March 18-25, 2006, La
Thuil
Dark energy, MOND and sub-millimeter tests of gravity
We consider modifications of General Relativity obtained by adding the
logarithm of some curvature invariants to the Einstein-Hilbert action. These
non-linear actions can explain the late-time acceleration of the universe
giving an expansion history that differs from that of a pure cosmological
constant. We show that they also modify the Newtonian potential below a fixed
acceleration scale given by the late-time Hubble constant times the speed of
light. This is exactly what is required in MOND, a phenomenological
modification of the Newtonian potential that is capable of explaining galactic
rotation curves without the need to introduce dark matter. We show that this
kind of modification also predicts short distance deviations of Newton's law at
the sub-mm scale and an anomalous shift in the precession of the Moon's orbit
around the Earth, both effects of a size that is less than an order of
magnitude below current bounds.Comment: 6 pages, to appear in proceedings of the XLIrst Rencontres de Morion
QCD perturbation theory at large orders with large renormalization scales in the large beta(0) limit
Chip-to-chip optical wireless link feasibility using optical phased arrays on silicon-on-insulator
One- and two-dimensional integrated optical phased arrays (OPAs) on silicon-on-insulator have been fabricated and measured having directivities of more than 40dBi and steering ranges up to 10 degrees . These OPAs would allow data rates of 100Mbps at distances up to 0.5m
Hamiltonian simulation of the Schwinger model at finite temperature
Using Matrix Product Operators (MPO) the Schwinger model is simulated in
thermal equilibrium. The variational manifold of gauge invariant MPO is
constructed to represent Gibbs states. As a first application the chiral
condensate in thermal equilibrium is computed and agreement with earlier
studies is found. Furthermore, as a new application the Schwinger model is
probed with a fractional charged static quark-antiquark pair separated
infinitely far from each other. A critical temperature beyond which the string
tension is exponentially suppressed is found, which is in qualitative agreement
with analytical studies in the strong coupling limit. Finally, the CT symmetry
breaking is investigated and our results strongly suggest that the symmetry is
restored at any nonzero temperature.Comment: Updated manuscript matching its published version: more detailed
continuum extrapolation of chiral condensate in section II
Tensor networks for gauge field theories
Over the last decade tensor network states (TNS) have emerged as a powerful
tool for the study of quantum many body systems. The matrix product states
(MPS) are one particular class of TNS and are used for the simulation of
(1+1)-dimensional systems. In this proceeding we use MPS to determine the
elementary excitations of the Schwinger model in the presence of an electric
background field. We obtain an estimate for the value of the background field
where the one-particle excitation with the largest energy becomes unstable and
decays into two other elementary particles with smaller energy.Comment: Proceeding of talk presented at the 33rd International Symposium on
Lattice Field Theory, 14-18 July 2015, Kobe, Japan; Proceeding of talk
presented at The European Physical Society Conference on High Energy Physics,
22-29 July 2015, Vienna, Austria (PoS(EPS-HEP2015)375
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