53,104 research outputs found
Renormalization group analysis of electrons near a Van Hove singularity.
A model of interacting two dimensional electrons near a Van Hove singularity
is studied, using renormalization group techniques. In hole doped systems, the
chemical potential is found to be pinned near the singularity, when the
electron-electron interactions are repulsive. The RG treatment of the leading
divergences appearing in perturbation theory give rise to marginal behavior and
anisotropic superconductivity.Comment: 4 Latex pages + 5 postcript figure
Electrostatic screening in fullerene molecules
The screening properties of fullerene molecules are described by means of a
continuum model which uses the electronic wavefunctions of planar graphite as a
starting point. The long distance behavior of the system gives rise to a
renormalizable theory, which flows towards a non trivial fixed point. Its
existence implies an anomalous dielectric constant. The screening properties
are neither metallic nor insulating. Alternatively, the intramolecular
screening is obtained from a simple approximation to the electronic
wavefunctions. Intermolecular effects are also calculated. As a consistency
check, it is shown that the observed polarizability of C is well
eproduced.Comment: 7 pages. Revte
Renormalizing Sznajd model on complex networks taking into account the effects of growth mechanisms
We present a renormalization approach to solve the Sznajd opinion formation
model on complex networks. For the case of two opinions, we present an
expression of the probability of reaching consensus for a given opinion as a
function of the initial fraction of agents with that opinion. The calculations
reproduce the sharp transition of the model on a fixed network, as well as the
recently observed smooth function for the model when simulated on a growing
complex networks.Comment: 5 pages, 7 figure
Few-anyon systems in a parabolic dot
The energy levels of two and three anyons in a two-dimensional parabolic
quantum dot and a perpendicular magnetic field are computed as power series in
1/|J|, where J is the angular momentum. The particles interact repulsively
through a coulombic (1/r) potential. In the two-anyon problem, the reached
accuracy is better than one part in 10^5. For three anyons, we study the
combined effects of anyon statistics and coulomb repulsion in the ``linear''
anyonic states.Comment: LaTeX, 6 pages, 4 postscript figure
Unpolarised Transverse Momentum Dependent Distribution and Fragmentation Functions from SIDIS Multiplicities
The unpolarised transverse momentum dependent distribution and fragmentation
functions are extracted from HERMES and COMPASS experimental measurements of
SIDIS multiplicities for charged hadron production. The data are grouped into
independent bins of the kinematical variables, in which the TMD factorisation
is expected to hold. A simple factorised functional form of the TMDs is
adopted, with a Gaussian dependence on the intrinsic transverse momentum, which
turns out to be quite adequate in shape. HERMES data do not need any
normalisation correction, while fits of the COMPASS data much improve with a
-dependent overall normalisation factor. A comparison of the extracted TMDs
with previous EMC and JLab data confirms the adequacy of the simple Gaussian
distributions. The possible role of the TMD evolution is briefly considered.Comment: 21 pages, 16 figure
Weyl geometry, anti-De Sitter space, and -theory
We study the Gaussian approximation to the quantum fluctuations of the metric
of the four dimensional anti-De Sitter spacetime. The associated massless
scalar field has a quartic self interaction, for which we construct the
generating functional of the -point correlation functions. The concomitant
infrared divergence is cured by a mass renormalization provided by the
cosmological constant, which is also responsible for the renormalization of the
coupling constant of the field theory.Comment: 9 pages, 1 figur
XMM-Newton and Deep Optical Observations of the OTELO fields: the Groth-Westphal Strip
OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with
the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be
the deepest and richest survey of emission line objects to date. The deep
narrow-band optical data from OSIRIS will be complemented by means of
additional observations that include: (i) an exploratory broad-band survey that
is already being carried out in the optical domain, (ii) FIR and sub-mm
observations to be carried with the Herschel space telescope and the GTM, and
(iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a
preliminary analysis of public EPIC data of one of the OTELO targets,the
Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC
images are combined with optical BVRI data from our broadband survey carried
out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving
X/O ratio, hardness ratios, B/T ratio) are tested.Comment: 2 pages, 2 figures, uses graphicx package. To appear in proceedings
of "The X-Ray Universe 2005", San Lorenzo del Escorial, Spain, September
26-30, 200
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
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