125 research outputs found
Hartree-Fock-Bogoliubov theory versus local-density approximation for superfluid trapped fermionic atoms
We investigate a gas of superfluid fermionic atoms trapped in two hyperfine
states by a spherical harmonic potential. We propose a new regularization
method to remove the ultraviolet divergence in the Hartree-Fock-Bogoliubov
equations caused by the use of a zero-range atom-atom interaction. Compared
with a method used in the literature, our method is simpler and has improved
convergence properties. Then we compare Hartree-Fock-Bogoliubov calculations
with the semiclassical local-density approximation. We observe that for systems
containing a small number of atoms shell effects, which cannot be reproduced by
the semiclassical calculation, are very important. For systems with a large
number of atoms at zero temperature the two calculations are in quite good
agreement, which, however, is deteriorated at non-zero temperature, especially
near the critical temperature. In this case the different behavior can be
explained within the Ginzburg-Landau theory.Comment: 12 pages, 8 figures, revtex; v2: references and clarifying remarks
adde
The future of social is personal: the potential of the personal data store
This chapter argues that technical architectures that facilitate the longitudinal, decentralised and individual-centric personal collection and curation of data will be an important, but partial, response to the pressing problem of the autonomy of the data subject, and the asymmetry of power between the subject and large scale service providers/data consumers. Towards framing the scope and role of such Personal Data Stores (PDSes), the legalistic notion of personal data is examined, and it is argued that a more inclusive, intuitive notion expresses more accurately what individuals require in order to preserve their autonomy in a data-driven world of large aggregators. Six challenges towards realising the PDS vision are set out: the requirement to store data for long periods; the difficulties of managing data for individuals; the need to reconsider the regulatory basis for third-party access to data; the need to comply with international data handling standards; the need to integrate privacy-enhancing technologies; and the need to future-proof data gathering against the evolution of social norms. The open experimental PDS platform INDX is introduced and described, as a means of beginning to address at least some of these six challenges
Status of a hybrid three-neutrino interpretation of neutrino data
We reanalyze the non-standard interaction (NSI) solutions to the solar
neutrino problem in the light of the latest solar, atmospheric and reactor
neutrino data. We show that such solutions, although preferred by the solar
data and consistent with the oscillation description of the atmospheric
neutrino data, are ruled out by the first results of the KamLAND reactor
experiment, at more than 3_sigma.Comment: 19 pages, LaTeX file using Elsart, 2 tables and 4 figures included.
This version updates the one published in Nucl.Phys.B629:479-490,2002 by
including the new KamLAND dat
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
Large-scale magnetic fields from inflation due to a -even Chern-Simons-like term with Kalb-Ramond and scalar fields
We investigate the generation of large-scale magnetic fields due to the
breaking of the conformal invariance in the electromagnetic field through the
-even dimension-six Chern-Simons-like effective interaction with a fermion
current by taking account of the dynamical Kalb-Ramond and scalar fields in
inflationary cosmology. It is explicitly demonstrated that the magnetic fields
on 1Mpc scale with the field strength of G at the present time
can be induced.Comment: 18 pages, 6 figures, version accepted for publication in Eur. Phys.
J.
Confusing non-standard neutrino interactions with oscillations at a neutrino factory
Most neutrino mass theories contain non-standard interactions (NSI) of
neutrinos which can be either non-universal (NU) or flavor-changing (FC). We
study the impact of such interactions on the determination of neutrino mixing
parameters at a neutrino factory using the so-called ``golden channels''
\pnu{e}\to\pnu{\mu} for the measurement of \theta_{13}. We show that a certain
combination of FC interactions in neutrino source and earth matter can give
exactly the same signal as oscillations arising due to \theta_{13}. This
implies that information about \theta_{13} can only be obtained if bounds on
NSI are available. Taking into account the existing bounds on FC interactions,
this leads to a drastic loss in sensitivity in \theta_{13}, at least two orders
of magnitude. A near detector at a neutrino factory offers the possibility to
obtain stringent bounds on some NSI parameters. Such near site detector
constitutes an essential ingredient of a neutrino factory and a necessary step
towards the determination of \theta_{13} and subsequent study of leptonic CP
violation.Comment: 23 pages, 5 figures, improved version, accepted for publication in
Phs. Rev. D, references adde
Neutrino masses: From fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are
coming close to reveal our fantasy: solar and atmospheric neutrino data
strongly indicate the need for neutrino conversions, while LSND provides an
intriguing hint. The simplest ways to reconcile these data in terms of neutrino
oscillations invoke a light sterile neutrino in addition to the three active
ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND
scale, while the others are at the solar mass scale. These schemes can be
distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments. I discuss the simplest theoretical scenarios, where the lightness
of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and
the generation of & all follow
naturally from the assumed lepton-number symmetry and its breaking. Although
the most likely interpretation of the present data is in terms of
neutrino-mass-induced oscillations, one still has room for alternative
explanations, such as flavour changing neutrino interactions, with no need for
neutrino mass or mixing. Such flavour violating transitions arise in theories
with strictly massless neutrinos, and may lead to other sizeable flavour
non-conservation effects, such as , conversion in
nuclei, unaccompanied by neutrino-less double beta decay.Comment: 33 pages, latex, 16 figures. Invited Talk at Ioannina Conference,
Symmetries in Intermediate High Energy Physics and its Applications, Oct.
1998, to be published by Springer Tracts in Modern Physics. Festschrift in
Honour of John Vergados' 60th Birthda
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
First measurements of azimuthal asymmetries in hadron-pair production in
deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron)
and NH_3 (proton) targets are presented. The data were taken in the years
2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c
at the CERN SPS. The asymmetries provide access to the transversity
distribution functions, without involving the Collins effect as in single
hadron production. The sizeable asymmetries measured on the NH_ target indicate
non-vanishing u-quark transversity and two-hadron interference fragmentation
functions. The small asymmetries measured on the ^6LiD target can be
interpreted as indication for a cancellation of u- and d-quark transversities.Comment: 13 pages, 4 figures, updated to the published versio
- …