2,554 research outputs found
Gravitational and electroweak unification by replacing diffeomorphisms with larger group
The covariance group for general relativity, the diffeomorphisms, is replaced
by a group of coordinate transformations which contains the diffeomorphisms as
a proper subgroup. The larger group is defined by the assumption that all
observers will agree whether any given quantity is conserved. Alternatively,
and equivalently, it is defined by the assumption that all observers will agree
that the general relativistic wave equation describes the propagation of light.
Thus, the group replacement is analogous to the replacement of the Lorentz
group by the diffeomorphisms that led Einstein from special relativity to
general relativity, and is also consistent with the assumption of constant
light velocity that led him to special relativity. The enlarged covariance
group leads to a non-commutative geometry based not on a manifold, but on a
nonlocal space in which paths, rather than points, are the most primitive
invariant entities. This yields a theory which unifies the gravitational and
electroweak interactions. The theory contains no adjustable parameters, such as
those that are chosen arbitrarily in the standard model.Comment: 28 pages
Nuclear spirals as feeding channels to the Supermassive Black Hole: the case of the galaxy NGC 6951
We report the discovery of gas streaming motions along nuclear spiral arms
towards the LINER nucleus of the galaxy NGC 6951. The observations, obtained
using the GMOS integral field spectrograph on the Gemini North telescope,
yielded maps of the flux distributions and gas kinematics in the Halpha,
[NII]6584 and [SII]6717,31 emission lines of the inner 7x5 arcsec^2 of the
galaxy. This region includes a circumnuclear star-forming ring with radius
500pc, a nuclear spiral inside the ring and the LINER nucleus. The kinematics
of the ionized gas is dominated by rotation, but subtraction of a kinematic
model of a rotating exponential disk reveals deviations from circular rotation
within the nuclear ring which can be attributed to (1) streaming motions along
the nuclear spiral arms and (2) a bipolar outflow which seems to be associated
to a nuclear jet. On the basis of the observed streaming velocities and
geometry of the spiral arms we estimate a mass inflow rate of ionized gas of
3x10^(-4) Msun/yr, which is of the order of the accretion rate necessary to
power the LINER nucleus of NGC 6951. Similar streaming motions towards the
nucleus of another galaxy with LINER nucleus -- NGC 1097 -- have been reported
by our group in a previous paper. Taken together, these results support a
scenario in which nuclear spirals are channels through which matter is
transferred from galactic scales to the nuclear region to feed the supermassive
black hole.Comment: 25 pages, 6 eps figures, accepted for publication in Ap
Non-standard Hamiltonian effects on neutrino oscillations
We investigate non-standard Hamiltonian effects on neutrino oscillations,
which are effective additional contributions to the vacuum or matter
Hamiltonian. Since these effects can enter in either flavor or mass basis, we
develop an understanding of the difference between these bases representing the
underlying theoretical model. In particular, the simplest of these effects are
classified as ``pure'' flavor or mass effects, where the appearance of such a
``pure'' effect can be quite plausible as a leading non-standard contribution
from theoretical models. Compared to earlier studies investigating particular
effects, we aim for a top-down classification of a possible ``new physics''
signature at future long-baseline neutrino oscillation precision experiments.
We develop a general framework for such effects with two neutrino flavors and
discuss the extension to three neutrino flavors, as well as we demonstrate the
challenges for a neutrino factory to distinguish the theoretical origin of
these effects with a numerical example. We find how the precision measurement
of neutrino oscillation parameters can be altered by non-standard effects alone
(not including non-standard interactions in the creation and detection
processes) and that the non-standard effects on Hamiltonian level can be
distinguished from other non-standard effects (such as neutrino decoherence and
decay) if we consider specific imprint of the effects on the energy spectra of
several different oscillation channels at a neutrino factory.Comment: 30 pages, 6 figures, LaTeX, final version, published in Eur.Phys.J.
Experimental observation of high field diamagnetic fluctuations in Niobium
We have performed a magnetic study of a bulk metallic sample of Nb with
critical temperature K. Magnetization versus temperature (M {\it
vs} T) data obtained for fixed magnetic fields above 1 kOe show a
superconducting transition which becomes broader as the field is increased. The
data are interpreted in terms of the diamagnetic lowest Landau level (LLL)
fluctuation theory. The scaling analysis gives values of the superconducting
transition temperature consistent with % . We search for
universal 3D LLL behavior by comparing scaling results for Nb and YBaCuO, but
obtain no evidence for universality.Comment: 5 pages, 6 figures, Accepted for publication in Phys.Rev.
Role of Brans-Dicke Theory with or without self-interacting potential in cosmic acceleration
In this work we have studied the possibility of obtaining cosmic acceleration
in Brans-Dicke theory with varying or constant (Brans- Dicke
parameter) and with or without self-interacting potential, the background fluid
being barotropic fluid or Generalized Chaplygin Gas. Here we take the power law
form of the scale factor and the scalar field. We show that accelerated
expansion can also be achieved for high values of for closed Universe.Comment: 12 Latex pages, 20 figures, RevTex styl
Early stage morphology of quench condensed Ag, Pb and Pb/Ag hybrid films
Scanning Tunneling Microscopy (STM) has been used to study the morphology of
Ag, Pb and Pb/Ag bilayer films fabricated by quench condensation of the
elements onto cold (T=77K), inert and atomically flat Highly Oriented Pyrolytic
Graphite (HOPG) substrates. All films are thinner than 10 nm and show a
granular structure that is consistent with earlier studies of QC films. The
average lateral diameter, , of the Ag grains, however, depends on
whether the Ag is deposited directly on HOPG ( = 13 nm) or on a Pb
film consisting of a single layer of Pb grains ( = 26.8 nm). In
addition, the critical thickness for electrical conduction () of Pb/Ag
films on inert glass substrates is substantially larger than for pure Ag films.
These results are evidence that the structure of the underlying substrate
exerts an influence on the size of the grains in QC films. We propose a
qualitative explanation for this previously unencountered phenomenon.Comment: 11 pages, 3 figures and one tabl
Bose-Einstein condensation in the presence of a uniform field and a point-like impurity
The behavior of an ideal -dimensional boson gas in the presence of a
uniform gravitational field is analyzed. It is explicitly shown that,
contrarily to an old standing folklore, the three-dimensional gas does not
undergo Bose-Einstein condensation at finite temperature. On the other hand,
Bose-Einstein condensation occurs at for if there is a
point-like impurity at the bottom of the vessel containing the gas.Comment: 14 pages, REVTEX. Revised version, accepted for publication in Phys.
Rev.
Randomized Reference Classifier with Gaussian Distribution and Soft Confusion Matrix Applied to the Improving Weak Classifiers
In this paper, an issue of building the RRC model using probability
distributions other than beta distribution is addressed. More precisely, in
this paper, we propose to build the RRR model using the truncated normal
distribution. Heuristic procedures for expected value and the variance of the
truncated-normal distribution are also proposed. The proposed approach is
tested using SCM-based model for testing the consequences of applying the
truncated normal distribution in the RRC model. The experimental evaluation is
performed using four different base classifiers and seven quality measures. The
results showed that the proposed approach is comparable to the RRC model built
using beta distribution. What is more, for some base classifiers, the
truncated-normal-based SCM algorithm turned out to be better at discovering
objects coming from minority classes.Comment: arXiv admin note: text overlap with arXiv:1901.0882
Anisotropic Magnetoconductance in Quench-Condensed Ultrathin Beryllium Films
Near the superconductor-insulator (S-I) transition, quench-condensed
ultrathin Be films show a large magnetoconductance which is highly anisotropic
in the direction of the applied field. Film conductance can drop as much as
seven orders of magnitude in a weak perpendicular field (< 1 T), but is
insensitive to a parallel field in the same field range. We believe that this
negative magnetoconductance is due to the field de-phasing of the
superconducting pair wavefunction. This idea enables us to extract the finite
superconducting phase coherence length in nearly superconducting films. Our
data indicate that this local phase coherence persists even in highly
insulating films in the vicinity of the S-I transition.Comment: 4 pages, 4 figure RevTex, Typos Correcte
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