3,026 research outputs found
Magnetic polarizability of hadrons from lattice QCD in the background field method
We present a calculation of hadron magnetic polarizability using the
techniques of lattice QCD. This is carried out by introducing a uniform
external magnetic field on the lattice and measuring the quadratic part of a
hadron's mass shift. The calculation is performed on a lattice with
standard Wilson actions at beta=6.0 (spacing fm) and pion mass down to
about 500 MeV. Results are obtained for 30 particles covering the entire baryon
octet (, , , , , , ,
) and decuplet (, , , ,
, , , , ,
), plus selected mesons (, , , , ,
, , , , , , ). The
results are compared with available values from experiments and other
theoretical calculations.Comment: 30 pages, 23 figures, 5 table
Uncovering the Internal Structure of the Indian Financial Market: Cross-correlation behavior in the NSE
The cross-correlations between price fluctuations of 201 frequently traded
stocks in the National Stock Exchange (NSE) of India are analyzed in this
paper. We use daily closing prices for the period 1996-2006, which coincides
with the period of rapid transformation of the market following liberalization.
The eigenvalue distribution of the cross-correlation matrix, , of
NSE is found to be similar to that of developed markets, such as the New York
Stock Exchange (NYSE): the majority of eigenvalues fall within the bounds
expected for a random matrix constructed from mutually uncorrelated time
series. Of the few largest eigenvalues that deviate from the bulk, the largest
is identified with market-wide movements. The intermediate eigenvalues that
occur between the largest and the bulk have been associated in NYSE with
specific business sectors with strong intra-group interactions. However, in the
Indian market, these deviating eigenvalues are comparatively very few and lie
much closer to the bulk. We propose that this is because of the relative lack
of distinct sector identity in the market, with the movement of stocks
dominantly influenced by the overall market trend. This is shown by explicit
construction of the interaction network in the market, first by generating the
minimum spanning tree from the unfiltered correlation matrix, and later, using
an improved method of generating the graph after filtering out the market mode
and random effects from the data. Both methods show, compared to developed
markets, the relative absence of clusters of co-moving stocks that belong to
the same business sector. This is consistent with the general belief that
emerging markets tend to be more correlated than developed markets.Comment: 15 pages, 8 figures, to appear in Proceedings of International
Workshop on "Econophysics & Sociophysics of Markets & Networks"
(Econophys-Kolkata III), Mar 12-15, 200
Hydrogen atom in a spherical well: linear approximation
We discuss the boundary effects on a quantum system by examining the problem
of a hydrogen atom in a spherical well. By using an approximation method which
is linear in energy we calculate the boundary corrections to the ground-state
energy and wave function. We obtain the asymptotic dependence of the
ground-state energy on the radius of the well.Comment: Revised version to appear in European Journal of Physic
Operator method in solving non-linear equations of the Hartree-Fock type
The operator method is used to construct the solutions of the problem of the
polaron in the strong coupling limit and of the helium atom on the basis of the
Hartree-Fock equation. is obtained for the polaron
ground-state energy. Energies for 2s- and 3s-states are also calculated. The
other excited states are briefly discussed.Comment: 7 page
Time evolution, cyclic solutions and geometric phases for general spin in an arbitrarily varying magnetic field
A neutral particle with general spin and magnetic moment moving in an
arbitrarily varying magnetic field is studied. The time evolution operator for
the Schr\"odinger equation can be obtained if one can find a unit vector that
satisfies the equation obeyed by the mean of the spin operator. There exist at
least cyclic solutions in any time interval. Some particular time
interval may exist in which all solutions are cyclic. The nonadiabatic
geometric phase for cyclic solutions generally contains extra terms in addition
to the familiar one that is proportional to the solid angle subtended by the
closed trace of the spin vector.Comment: revtex4, 8 pages, no figur
Nuclear Octupole Correlations and the Enhancement of Atomic Time-Reversal Violation
We examine the time-reversal-violating nuclear ``Schiff moment'' that induces
electric dipole moments in atoms. After presenting a self-contained derivation
of the form of the Schiff operator, we show that the distribution of Schiff
strength, an important ingredient in the ground-state Schiff moment, is very
different from the electric-dipole-strength distribution, with the Schiff
moment receiving no strength from the giant dipole resonance in the
Goldhaber-Teller model. We then present shell-model calculations in light
nuclei that confirm the negligible role of the dipole resonance and show the
Schiff strength to be strongly correlated with low-lying octupole strength.
Next, we turn to heavy nuclei, examining recent arguments for the strong
enhancement of Schiff moments in octupole-deformed nuclei over that of 199Hg,
for example. We concur that there is a significant enhancement while pointing
to effects neglected in previous work (both in the octupole-deformed nuclides
and 199Hg) that may reduce it somewhat, and emphasizing the need for
microscopic calculations to resolve the issue. Finally, we show that static
octupole deformation is not essential for the development of collective Schiff
moments; nuclei with strong octupole vibrations have them as well, and some
could be exploited by experiment.Comment: 25 pages, 4 figures embedded in tex
Decuplet Baryon Structure from Lattice QCD
The electromagnetic properties of the SU(3)-flavor baryon decuplet are
examined within a lattice simulation of quenched QCD. Electric charge radii,
magnetic moments, and magnetic radii are extracted from the E0 and M1 form
factors. Preliminary results for the E2 and M3 moments are presented giving the
first model independent insight to the shape of the quark distribution in the
baryon ground state. As in our octet baryon analysis, the lattice results give
evidence of spin-dependent forces and mass effects in the electromagnetic
properties. The quark charge distribution radii indicate these effects act in
opposing directions. Some baryon dependence of the effective quark magnetic
moments is seen. However, this dependence in decuplet baryons is more subtle
than that for octet baryons. Of particular interest are the lattice predictions
for the magnetic moments of and for which new recent
experimental measurements are available. The lattice prediction of the
ratio appears larger than the experimental ratio, while the
lattice prediction for the magnetic moment ratio is in good
agreement with the experimental ratio.Comment: RevTeX manuscript, 34 pages plus 21 figures (available upon request
Solvable three-state model of a driven double-well potential and coherent destruction of tunneling
A simple model for a particle in a double well is derived from discretizing its configuration space. The model contains as many free parameters as the original system and it respects all the existing symmetries. In the presence of an external periodic force both the continuous system and the discrete model are shown to possess a generalized time-reversal symmetry in addition to the known generalized parity. The impact of the driving force on the spectrum of the Floquet operator is studied. In particular, the occurrence of degenerate quasienergies causing coherent destruction of tunneling is discussed—to a large extent analytically—for arbitrary driving frequencies and barrier heights
A Perturbative/Variational Approach to Quantum Lattice Hamiltonians
We propose a method to construct the ground state of local
lattice hamiltonians with the generic form , where
is a coupling constant and is a hamiltonian with a non degenerate ground
state . The method is based on the choice of an exponential ansatz
, which is a sort of generalized
lattice version of a Jastrow wave function. We combine perturbative and
variational techniques to get succesive approximations of the operator
. Perturbation theory is used to set up a variational method which
in turn produces non perturbative results. The computation with this kind of
ansatzs leads to associate to the original quantum mechanical problem a
statistical mechanical system defined in the same spatial dimension. In some
cases these statistical mechanical systems turn out to be integrable, which
allow us to obtain exact upper bounds to the energy. The general ideas of our
method are illustrated in the example of the Ising model in a transverse field.Comment: 27 pages, three .ps figures appended, DFTUZ 94-2
Time evolution, cyclic solutions and geometric phases for the generalized time-dependent harmonic oscillator
The generalized time-dependent harmonic oscillator is studied. Though several
approaches to the solution of this model have been available, yet a new
approach is presented here, which is very suitable for the study of cyclic
solutions and geometric phases. In this approach, finding the time evolution
operator for the Schr\"odinger equation is reduced to solving an ordinary
differential equation for a c-number vector which moves on a hyperboloid in a
three-dimensional space. Cyclic solutions do not exist for all time intervals.
A necessary and sufficient condition for the existence of cyclic solutions is
given. There may exist some particular time interval in which all solutions
with definite parity, or even all solutions, are cyclic. Criterions for the
appearance of such cases are given. The known relation that the nonadiabatic
geometric phase for a cyclic solution is proportional to the classical Hannay
angle is reestablished. However, this is valid only for special cyclic
solutions. For more general ones, the nonadiabatic geometric phase may contain
an extra term. Several cases with relatively simple Hamiltonians are solved and
discussed in detail. Cyclic solutions exist in most cases. The pattern of the
motion, say, finite or infinite, can not be simply determined by the nature of
the Hamiltonian (elliptic or hyperbolic, etc.). For a Hamiltonian with a
definite nature, the motion can changes from one pattern to another, that is,
some kind of phase transition may occur, if some parameter in the Hamiltonian
goes through some critical value.Comment: revtex4, 28 pages, no figur
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