18,911 research outputs found
One-loop mass shift formula for kinks and self-dual vortices
A formula is derived that allows us to compute one-loop mass shifts for kinks
and self-dual Abrikosov-Nielsen-Olesen vortices. The procedure is based in
canonical quantization and heat kernel/zeta function regularization methods.Comment: LaTex file, 8 pages, 1 figure . Based on a talk given by J. M. G. at
the 7th Workshop on Quantum Field Theory under the Influence of External
Conditions (QFEXT05), Barcelona, Spain. Minor corrections. Version to appear
in Journal of Physics
Quantum fluctuations around low-dimensional topological defects
In these Lectures a method is described to analyze the effect of quantum
fluctuations on topological defect backgrounds up to the one-loop level. The
method is based on the spectral heat kernel/zeta function regularization
procedure, and it is first applied to various types of kinks arising in several
deformed linear and non-linear sigma models with different numbers of scalar
fields. In the second part, the same conceptual framework is constructed for
the topological solitons of the planar semilocal Abelian Higgs model, built
from a doublet of complex scalar fields and one U(1) gauge field.Comment: 63 pages, 14 figures, expanded version of two lectures given by
J.M.G. in 5th International School on Field Theory and Gravitation, Cuiaba,
Brazi
Quantum corrections to the mass of self-dual vortices
The mass shift induced by one-loop quantum fluctuations on self-dual ANO
vortices is computed using heat kernel/generalized zeta function regularization
methods.Comment: 4 pages RevTex, version to appear in Physical Review
Magnetization Process of Single Molecule Magnets at Low Temperatures
We show that correlations established before quenching to very low
temperatures, later drive the magnetization process of systems of single
molecule magnets, after a magnetic field is applied at t=0. We also show that
in SC lattices, m \propto sqrt(t), as observed in Fe_8, but only for
1+2*log_10(h_d/h_w) time decades, where h_d is a nearest neighbor dipolar
magnetic field and a spin reversal can occur only if the field on it is within
(-h_w,h_w). However, the sqrt(t) behavior is not universal. For BCC and FCC
lattices, m \propto t^p, but p \simeq 0.7. The value to which m finally levels
off is also given.Comment: 5 LaTeX pages, 2 figures. Submitted to Phys. Rev. Lett. on 26 January
2003, accepted on 24 July 200
Friedel Oscillations in Relativistic Nuclear Matter
We calculate the low-momentum N-N effective potential obtained in the OBE
approximation, inside a nuclear plasma at finite temperature, as described by
the relativistic - model. We analyze the screening effects
on the attractive part of the potential in the intermediate range as density or
temperature increase. In the long range the potential shows Friedel-like
oscillations instead of the usual exponential damping. These oscillations arise
from the sharp edge of the Fermi surface and should be encountered in any
realistic model of nuclear matter.Comment: 11 pages in preprint format, typeset using REVTEX, 3 included figures
in tar, compressed, uuencoded forma
Time-dependent density functional theory calculation of van der Waals coefficient of sodium clusters
In this paper we employ all-electron \textit{ab-initio} time-dependent
density functional theory based method to calculate the long range
dipole-dipole dispersion coefficient (van der Waals coefficient) of
sodium atom clusters containing even number of atoms ranging from 2 to 20
atoms. The dispersion coefficients are obtained via Casimir-Polder relation.
The calculations are carried out with two different exchange-correlation
potentials: (i) the asymptotically correct statistical average of orbital
potential (SAOP) and (ii) Vosko-Wilk-Nusair representation of
exchange-correlation potential within local density approximation. A comparison
with the other theoretical results has been performed. We also present the
results for the static polarizabilities of sodium clusters and also compare
them with other theoretical and experimental results. These comparisons reveal
that the SAOP results for C_{6} and static polarizability are quite accurate
and very close to the experimental results. We examine the relationship between
volume of the cluster and van der Waals coefficient and find that to a very
high degree of correlation C_{6} scales as square of the volume. We also
present the results for van der Waals coefficient corresponding to cluster-Ar
atom and cluster-N_{2} molecule interactions.Comment: 22 pages including 6 figures. To be published in Journal of Chemical
Physic
Cyclotrons as Drivers for Precision Neutrino Measurements
As we enter the age of precision measurement in neutrino physics, improved
flux sources are required. These must have a well-defined flavor content with
energies in ranges where backgrounds are low and cross section knowledge is
high. Very few sources of neutrinos can meet these requirements. However,
pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for
decay-at-rest sources are cyclotron accelerators, which are compact and
relatively inexpensive. This paper describes a scheme to produce decay-at-rest
sources driven by such cyclotrons, developed within the DAEdALUS program.
Examples of the value of the high precision beams for pursuing Beyond Standard
Model interactions are reviewed. New results on a combined DAEdALUS--Hyper-K
search for CP-violation that achieve errors on the mixing matrix parameter of 4
degrees to 12 degrees are presented.Comment: This paper was invited by the journal Advances in High Energy Physics
for their upcoming special issue on "Neutrino Masses and Oscillations," which
will be published on the 100th anniversary of Pontecorvo's birt
The Spectrum of Pluto, 0.40 - 0.93 m I. Secular and longitudinal distribution of ices and complex organics
Context. During the last 30 years the surface of Pluto has been
characterized, and its variability has been monitored, through continuous
near-infrared spectroscopic observations. But in the visible range only few
data are available. Aims. The aim of this work is to define the Pluto's
relative reflectance in the visible range to characterize the different
components of its surface, and to provide ground based observations in support
of the New Horizons mission. Methods. We observed Pluto on six nights between
May and July 2014, with the imager/spectrograph ACAM at the William Herschel
Telescope (La Palma, Spain). The six spectra obtained cover a whole rotation of
Pluto (Prot = 6.4 days). For all the spectra we computed the spectral slope and
the depth of the absorption bands of methane ice between 0.62 and 0.90 m.
To search for shifts of the center of the methane bands, associated with
dilution of CH4 in N2, we compared the bands with reflectances of pure methane
ice. Results. All the new spectra show the methane ice absorption bands between
0.62 and 0.90 m. The computation of the depth of the band at 0.62 m
in the new spectra of Pluto, and in the spectra of Makemake and Eris from the
literature, allowed us to estimate the Lambert coefficient at this wavelength,
at a temperature of 30 K and 40 K, never measured before. All the detected
bands are blue shifted, with minimum shifts in correspondence with the regions
where the abundance of methane is higher. This could be indicative of a
dilution of CH4:N2 more saturated in CH4. The longitudinal and secular
variations of the parameters measured in the spectra are in accordance with
results previously reported in the literature and with the distribution of the
dark and bright material that show the Pluto's albedo maps from New Horizons.Comment: This manuscript may change and improve during the reviewing process.
The data reduction and calibration is reliable and has been checked
independently using different reduction approaches. The data will be made
publicily available when the paper is accepted. If you need them before,
please, contact the autho
The VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge
Solid insight into the physics of the inner Milky Way is key to understanding
our Galaxy's evolution, but extreme dust obscuration has historically hindered
efforts to map the area along the Galactic mid-plane. New comprehensive
near-infrared time-series photometry from the VVV Survey has revealed 35
classical Cepheids, tracing a previously unobserved component of the inner
Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic
mid-plane, traversing across the bulge. The discovered period (age) spread of
these classical Cepheids implies a continuous supply of newly formed stars in
the central region of the Galaxy over the last 100 million years.Comment: Accepted for publication in The Astrophysical Journal Letters.
Near-IR finding charts of the Cepheids are available at the following URL:
http://www.astro.puc.cl/~idekany/pub/inner_disk_ceph_fc.pn
Magic Numbers for the Photoelectron Anisotropy in Li-Doped Dimethyl Ether Clusters
Photoelectron velocity map imaging of Li(CHOCH) clusters (1
n 175) is used to search for magic numbers related to the
photoelectron anisotropy. Comparison with density functional calculations
reveals magic numbers at n=4, 5, and 6, resulting from the symmetric charge
distribution with high s-character of the highest occupied molecular orbital.
Since each of these three cluster sizes correspond to the completion of a first
coordination shell, they can be considered as 'isomeric motifs of the first
coordination shell'. Differences in the photoelectron anisotropy, the vertical
ionization energies and the enthalpies of vaporization between
Li(CHOCH) and Na(CHOCH) can be rationalized in terms of
differences in their solvation shells, atomic ionization energies,
polarizabilities, metal-oxygen bonds, ligand-ligand interactions, and by
cooperative effects
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