61,738 research outputs found
Continuum damage mechanics model as an instrument for development of design rules for steel structures in seismic affected zones
Full QCD calculation of neutron electric dipole moment with the external electric field method
We have calculated the neutron electric dipole moment (NEDM) in the presence
of the CP violating term in lattice QCD with 2-flavor dynamical clover
quarks, using the external electric field method. Accumulating a large number
of statistics by the averages over 16 different source points and over forward
and backward nucleon propagators, we have obtained non-zero signals of neutron
and proton EDM beyond one standard deviation at each quark mass in full QCD. We
have investigated the quark mass dependence of nucleon EDM in full QCD, and
have found that nucleon EDM in full QCD does not decrease toward the chiral
limit, as opposed to the theoretical expectation. We briefly discuss possible
reasons for this behavior.Comment: 27 pages, 15 figures, 2 tables, reference added, tyops corrected,
published versio
Melting and unzipping of DNA
Experimental studies of the thermal denaturation of DNA yield a strong
indication that the transition is first order. This transition has been
theoretically studied since the early sixties, mostly within an approach in
which the microscopic configurations of a DNA molecule are given by an
alternating sequence of non-interacting bound segments and denaturated loops.
Studies of these models neglect the repulsive, self-avoiding, interaction
between different loops and segments and have invariably yielded continuous
denaturation transitions. In this study we exploit recent results on scaling
properties of polymer networks of arbitrary topology in order to take into
account the excluded-volume interaction between denaturated loops and the rest
of the chain. We thus obtain a first-order phase transition in d=2 dimensions
and above, in agreement with experiments. We also consider within our approach
the unzipping transition, which takes place when the two DNA strands are pulled
apart by an external force acting on one end. We find that the unzipping
transition is also first order. Although the denaturation and unzipping
transitions are thermodynamically first order, they do exhibit critical
fluctuations in some of their properties. For instance, the loop size
distribution decays algebraically at the transition and the length of the
denaturated end segment diverges as the transition is approached. We evaluate
these critical properties within our approach.Comment: 12pages,8 figures, REVTEX
Spontaneous polarisation of the neutral interface for valence asymmetric coulombic systems
In this paper, we discuss the phenomenon of a spontaneous polarisation of a
neutral hard planar interface for valence asymmetric coulombic systems. Within
a field theoretical description, we account for the existence of non trivial
charge density and electric potential profiles. The analysis of the phenomenon
shows that the effect is related to combinatorics in relation with the
existence of the two independent species cations and anions. This simple and
basic feature is related to the quantum mechanical properties of the system.
The theoretical results are compared with numerical simulations data and are
shown to be in very good agreement, which a fortiori justifies our physical
interpretation.Comment: 12 pages, 11 figure
Random quantum magnets with broad disorder distribution
We study the critical behavior of Ising quantum magnets with broadly
distributed random couplings (J), such that , , for large (L\'evy flight statistics).
For sufficiently broad distributions, , the critical behavior
is controlled by a line of fixed points, where the critical exponents vary with
the L\'evy index, . In one dimension, with , we obtaind
several exact results through a mapping to surviving Riemann walks. In two
dimensions the varying critical exponents have been calculated by a numerical
implementation of the Ma-Dasgupta-Hu renormalization group method leading to
. Thus in the region , where the
central limit theorem holds for the broadness of the distribution is
relevant for the 2d quantum Ising model.Comment: 10pages, 13figures, final for
Dynamics of viscous dissipative gravitational collapse: A full causal approach
The Misner and Sharp approach to the study of gravitational collapse is
extended to the viscous dissipative case in, both, the streaming out and the
diffusion approximations. The dynamical equation is then coupled to causal
transport equations for the heat flux, the shear and the bulk viscosity, in the
context of Israel--Stewart theory, without excluding the thermodynamics
viscous/heat coupling coefficients. The result is compared with previous works
where these later coefficients were neglected and viscosity variables were not
assumed to satisfy causal transport equations. Prospective applications of this
result to some astrophysical scenarios are discussed.Comment: 22 pages Latex. To appear in Int. J. Mod. Phys. D. Typos correcte
Formation and observation of a quasi-two-dimensional electron liquid in epitaxially stabilized SrLaTiO thin films
We report the formation and observation of an electron liquid in
SrLaTiO, the quasi-two-dimensional counterpart of SrTiO,
through reactive molecular-beam epitaxy and {\it in situ} angle-resolved
photoemission spectroscopy. The lowest lying states are found to be comprised
of Ti 3 orbitals, analogous to the LaAlO/SrTiO interface and
exhibit unusually broad features characterized by quantized energy levels and a
reduced Luttinger volume. Using model calculations, we explain these
characteristics through an interplay of disorder and electron-phonon coupling
acting co-operatively at similar energy scales, which provides a possible
mechanism for explaining the low free carrier concentrations observed at
various oxide heterostructures such as the LaAlO/SrTiO interface
Folding of the Triangular Lattice in the FCC Lattice with Quenched Random Spontaneous Curvature
We study the folding of the regular two-dimensional triangular lattice
embedded in the regular three-dimensional Face Centered Cubic lattice, in the
presence of quenched random spontaneous curvature. We consider two types of
quenched randomness: (1) a ``physical'' randomness arising from a prior random
folding of the lattice, creating a prefered spontaneous curvature on the bonds;
(2) a simple randomness where the spontaneous curvature is chosen at random
independently on each bond. We study the folding transitions of the two models
within the hexagon approximation of the Cluster Variation Method. Depending on
the type of randomness, the system shows different behaviors. We finally
discuss a Hopfield-like model as an extension of the physical randomness
problem to account for the case where several different configurations are
stored in the prior pre-folding process.Comment: 12 pages, Tex (harvmac.tex), 4 figures. J.Phys.A (in press
Neutron electric dipole moment from lattice QCD
We carry out a feasibility study for the lattice QCD calculation of the
neutron electric dipole moment (NEDM) in the presence of the term. We
develop the strategy to obtain the nucleon EDM from the CP-odd electromagnetic
form factor at small , in which NEDM is given by where is the momentum transfer and is the
nucleon mass. We first derive a formula which relates , a matrix element
of the electromagnetic current between nucleon states, with vacuum expectation
values of nucleons and/or the current. In the expansion of , the
parity-odd part of the nucleon-current-nucleon three-point function contains
contributions not only from the parity-odd form factors but also from the
parity-even form factors multiplied by the parity-odd part of the nucleon
two-point function, and therefore the latter contribution must be subtracted to
extract . We then perform an explicit lattice calculation employing the
domain-wall quark action with the RG improved gauge action in quenched QCD at
GeV on a lattice. At the quark mass
, corresponding to , we accumulate 730
configurations, which allow us to extract the parity-odd part in both two- and
three-point functions. Employing two different Dirac matrix
projections, we show that a consistent value for cannot be obtained
without the subtraction described above. We obtain 0.024(5) fm for the neutron and
0.021(6) fm for the
proton.Comment: LaTeX2e, 43 pages, 42 eps figures, uses revtex4 and graphicx,
comments added and typos corrected, final version to appear in Phys. Rev.
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