44,518 research outputs found
Renormalization group and Ward identities in quantum liquid phases and in unconventional critical phenomena
By reviewing the application of the renormalization group to different
theoretical problems, we emphasize the role played by the general symmetry
properties in identifying the relevant running variables describing the
behavior of a given physical system. In particular, we show how the constraints
due to the Ward identities, which implement the conservation laws associated
with the various symmetries, help to minimize the number of independent running
variables. This use of the Ward identities is examined both in the case of a
stable phase and of a critical phenomenon. In the first case we consider the
problems of interacting fermions and bosons. In one dimension general and
specific Ward identities are sufficient to show the non-Fermi-liquid character
of the interacting fermion system, and also allow to describe the crossover to
a Fermi liquid above one dimension. This crossover is examined both in the
absence and presence of singular interaction. On the other hand, in the case of
interacting bosons in the superfluid phase, the implementation of the Ward
identities provides the asymptotically exact description of the acoustic
low-energy excitation spectrum, and clarifies the subtle mechanism of how this
is realized below and above three dimensions. As a critical phenomenon, we
discuss the disorder-driven metal-insulator transition in a disordered
interacting Fermi system. In this case, through the use of Ward identities, one
is able to associate all the disorder effects to renormalizations of the Landau
parameters. As a consequence, the occurrence of a metal-insulator transition is
described as a critical breakdown of a Fermi liquid.Comment: 47 pages, 11 figure
Entanglement of two-qubit photon beam by magnetic field
We have studied the possibility of affecting the entanglement measure of
2-qubit system consisting of two photons with different fixed frequencies but
with two arbitrary linear polarizations, moving in the same direction, by the
help of an applied external magnetic field. The interaction between the
magnetic field and the photons in our model is achieved through intermediate
electrons that interact with both the photons and the magnetic field. The
possibility of exact theoretical analysis of this scheme is based on known
exact solutions that describe the interaction of an electron subjected to an
external magnetic field (or a medium of electrons not interacting with each
other) with a quantized field of two photons. We adapt these exact solutions to
the case under consideration. Using explicit wave functions for the resulting
electromagnetic field, we calculate the entanglement measure of the photon beam
as a function of the applied magnetic field and parameters of the electron
medium
String Representation of Quantum Loops
We recover a general representation for the quantum state of a relativistic
closed line (loop) in terms of string degrees of freedom.The general form of
the loop functional splits into the product of the Eguchi functional, encoding
the holographic quantum dynamics, times the Polyakov path integral, taking into
account the full Bulk dynamics, times a loop effective action, which is needed
to renormalize boundary ultraviolet divergences. The Polyakov string action is
derived as an effective actionfrom a phase space,covariant,Schild action, by
functionally integrating out the world-sheet coordinates.The area coordinates
description of the boundary quantum dynamics, is shown to be induced by the
``zero mode'' of the bulk quantum fluctuations. Finally, we briefly comment
about a ``unified, fully covariant'' description of points, loops and strings
in terms of Matrix Coordinates.Comment: 16 Pages, RevTeX, no figure
Dirac Fermion Confinement in Graphene
We study the problem of Dirac fermion confinement in graphene in the presence
of a perpendicular magnetic field B. We show, analytically and numerically,
that confinement leads to anomalies in the electronic spectrum and to a
magnetic field dependent crossover from \sqrt{B}, characteristic of
Dirac-Landau level behavior, to linear in B behavior, characteristic of
confinement. This crossover occurs when the radius of the Landau level becomes
of the order of the width of the system. As a result, we show that the
Shubnikov-de Haas oscillations also change as a function of field, and lead to
a singular Landau plot. We show that our theory is in excellent agreement with
the experimental data.Comment: 4 pages, 6 figure
Comparative Genomics Analysis of a New Exiguobacterium Strain from Salar de Huasco Reveals a Repertoire of Stress-Related Genes and Arsenic Resistance
Indexación: Web of Science; Scopus.The Atacama Desert hosts diverse ecosystems including salt flats and shallow Andean lakes. Several heavy metals are found in the Atacama Desert, and microorganisms growing in this environment show varying levels of resistance/tolerance to copper, tellurium, and arsenic, among others. Herein, we report the genome sequence and comparative genomic analysis of a new Exiguobacterium strain, sp. SH31, isolated from an altiplanic shallow athalassohaline lake. Exiguobacterium sp. SH31 belongs to the phylogenetic Group II and its closest relative is Exiguobacterium sp. S17, isolated from the Argentinian Altiplano (95% average nucleotide identity). Strain SH31 encodes a wide repertoire of proteins required for cadmium, copper, mercury, tellurium, chromium, and arsenic resistance. Of the 34 Exiguobacterium genomes that were inspected, only isolates SH31 and S17 encode the arsenic efflux pump Acr3. Strain SH31 was able to grow in up to 10 mM arsenite and 100 mM arsenate, indicating that it is arsenic resistant. Further, expression of the ars operon and acr3 was strongly induced in response to both toxics, suggesting that the arsenic efflux pump Acr3 mediates arsenic resistance in Exiguobacterium sp. SH31.http://journal.frontiersin.org/article/10.3389/fmicb.2017.00456/ful
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