5,987 research outputs found
Reply to "Comment on 'Gravitating Magnetic Monopole in the Global Monopole Spacetime' "
In this Reply I present some arguments in favor of the stability of the
topological defect composed by global and magnetic monopoles.Comment: 1 page, no figures. Revised version improves the theoretical analysis
about electrostatic self-interaction in the global monopole spacetim
Theory of the Fermi Arcs, the Pseudogap, and the Anisotropy in k-space of Cuprate Superconductors
The appearance of the Fermi arcs or gapless regions at the nodes of the Fermi
surface just above the critical temperature is described through
self-consistent calculations in an electronic disordered medium. We develop a
model for cuprate superconductors based on an array of Josephson junctions
formed by grains of inhomogeneous electronic density derived from a phase
separation transition. This approach provides physical insights to the most
important properties of these materials like the pseudogap phase as forming by
the onset of local (intragrain) superconducting amplitudes and the zero
resistivity critical temperature due to phase coherence activated by
Josephson coupling. The formation of the Fermi arcs and the dichotomy in
k-space follows from the direction dependence of the junctions tunneling
current on the d-wave symmetry on the planes. We show that this
semi-phenomenological approach reproduces also the main future of the cuprates
phase diagram.Comment: 5 pages 7 fig
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
A double coset ansatz for integrability in AdS/CFT
We give a proof that the expected counting of strings attached to giant
graviton branes in AdS_5 x S^5, as constrained by the Gauss Law, matches the
dimension spanned by the expected dual operators in the gauge theory. The
counting of string-brane configurations is formulated as a graph counting
problem, which can be expressed as the number of points on a double coset
involving permutation groups. Fourier transformation on the double coset
suggests an ansatz for the diagonalization of the one-loop dilatation operator
in this sector of strings attached to giant graviton branes. The ansatz agrees
with and extends recent results which have found the dynamics of open string
excitations of giants to be given by harmonic oscillators. We prove that it
provides the conjectured diagonalization leading to harmonic oscillators.Comment: 33 pages, 3 figures; v2: references adde
Measurements and analysis of the upper critical field on an underdoped and overdoped compounds
The upper critical field is one of the many non conventional
properties of high- cuprates. It is possible that the
anomalies are due to the presence of inhomogeneities in the local charge
carrier density of the planes. In order to study this point, we
have prepared good quality samples of polycrystalline
using the wet-chemical method, which has demonstrated to produce samples with a
better cation distribution. In particular, we have studied the temperature
dependence of the second critical field, , through the magnetization
measurements on two samples with opposite average carrier concentration
() and nearly the same critical temperature, namely
(underdoped) and (overdoped). The results close to do not
follow the usual Ginzburg-Landau theory and are interpreted by a theory which
takes into account the influence of the inhomogeneities.Comment: Published versio
Solving Four Dimensional Field Theories with the Dirichlet Fivebrane
The realization of four dimensional super Yang-Mills theories in
terms of a single Dirichlet fivebrane in type IIB string theory is considered.
A classical brane computation reproduces the full quantum low energy effective
action. This result has a simple explanation in terms of mirror symmetry.Comment: Final version to appear in Phys. Rev.
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