5,287 research outputs found
SU(3)_LxU(1)_N Model for Right-Handed Neutrino Neutral Currents
A model based on the \mbox{SU(3)}_L\otimes \mbox{U(1)}_N gauge group, in
which neutrinos have right-handed neutral currents is considered. We argue that
in order to have a result consistent with low-energy one, the right-handed
neutrino component must be treated as correction instead of an equivalent spin
state.Comment: 6 pages, Latex, no figures, Accepted for publication in Phys. Rev.
Forward-backward equations for nonlinear propagation in axially-invariant optical systems
We present a novel general framework to deal with forward and backward
components of the electromagnetic field in axially-invariant nonlinear optical
systems, which include those having any type of linear or nonlinear transverse
inhomogeneities. With a minimum amount of approximations, we obtain a system of
two first-order equations for forward and backward components explicitly
showing the nonlinear couplings among them. The modal approach used allows for
an effective reduction of the dimensionality of the original problem from 3+1
(three spatial dimensions plus one time dimension) to 1+1 (one spatial
dimension plus one frequency dimension). The new equations can be written in a
spinor Dirac-like form, out of which conserved quantities can be calculated in
an elegant manner. Finally, these new equations inherently incorporate
spatio-temporal couplings, so that they can be easily particularized to deal
with purely temporal or purely spatial effects. Nonlinear forward pulse
propagation and non-paraxial evolution of spatial structures are analyzed as
examples.Comment: 11 page
Particle dispersion processes in two-dimensional turbulence: a comparison with 2-D kinematic simulation.
International audienceWe study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due to the absence of strong coherent vortices and advection processes in the KS fields. The comparison allows to refine past studies about the contribution of non-homogeneous space-time 2-D Eulerian structure on the turbulent absolute and relative particle dispersion processes. We particularly focus our discussion on the Richardson's regime for relative dispersion
Remark on the vectorlike nature of the electromagnetism and the electric charge quantization
In this work we study the structure of the electromagnetic interactions and
the electric charge quantization in gauge theories of electroweak interactions
based on semi-simple groups. We show that in the standard model of the
electroweak interactions the structure of the electromagnetic interactions is
strongly correlated to the quantization pattern of the electric charges. We
examine these two questions also in all possible chiral bilepton gauge models
of the electroweak interactions. In all they we can explain the vectorlike
nature of the electromagnetic interactions and the electric charge quantization
together demanding nonvanishing fermion masses and the anomaly cancellations.Comment: 17 pages, latex, no figure
Dual Interpretations of Seiberg-Witten and Dijkgraaf-Vafa curves
We give dual interpretations of Seiberg-Witten and Dijkgraaf-Vafa (or matrix
model) curves in n=1 supersymmetric U(N) gauge theory. This duality
interchanges the rank of the gauge group with the degree of the superpotential;
moreover, the constraint of having at most log-normalizable deformations of the
geometry is mapped to a constraint in the number of flavors N_f < N in the dual
theory.Comment: Latex2e, 22 pages, 2 figure
Diffstar: A Fully Parametric Physical Model for Galaxy Assembly History
We present Diffstar, a smooth parametric model for the in-situ star formation
history (SFH) of galaxies. Diffstar is distinct from conventional SFH models
that are used to interpret the spectral energy distribution (SED) of an
observed galaxy, because our model is parametrized directly in terms of basic
features of galaxy formation physics. The Diffstar model assumes that star
formation is fueled by the accretion of gas into the dark matter halo of the
galaxy, and at the foundation of Diffstar is a parametric model for halo mass
assembly, Diffmah. We include parametrized ingredients for the fraction of
accreted gas that is eventually transformed into stars,
and for the timescale over which this transformation occurs,
some galaxies in Diffstar experience a quenching event at time and
may subsequently experience rejuvenated star formation. We fit the SFHs of
galaxies predicted by the IllustrisTNG (TNG) and UniverseMachine (UM)
simulations with the Diffstar parameterization, and show that our model is
sufficiently flexible to describe the average stellar mass histories of
galaxies in both simulations with an accuracy of dex across most of
cosmic time. We use Diffstar to compare TNG to UM in common physical terms,
finding that: (i) star formation in UM is less efficient and burstier relative
to TNG; (ii) galaxies in UM have longer gas consumption timescales, , relative to TNG; (iii) rejuvenated star formation is ubiquitous in UM,
whereas quenched TNG galaxies rarely experience sustained rejuvenation; and
(iv) in both simulations, the distributions of , , and share a common characteristic dependence upon halo
mass, and present significant correlations with halo assembly history.
[Abridged]Comment: 26 pages, 21 figure
Fixed points and vacuum energy of dynamically broken gauge theories
We show that if a gauge theory with dynamical symmetry breaking has
non-trivial fixed points, they will correspond to extrema of the vacuum energy.
This relationship provides a different method to determine fixed points.Comment: 17 pages, uuencoded latex file, 3 figures, uses epsf and epsfig.
Submitted to Mod. Phys. Lett.
Entropy of the Nordic electricity market: anomalous scaling, spikes, and mean-reversion
The electricity market is a very peculiar market due to the large variety of
phenomena that can affect the spot price. However, this market still shows many
typical features of other speculative (commodity) markets like, for instance,
data clustering and mean reversion. We apply the diffusion entropy analysis
(DEA) to the Nordic spot electricity market (Nord Pool). We study the waiting
time statistics between consecutive spot price spikes and find it to show
anomalous scaling characterized by a decaying power-law. The exponent observed
in data follows a quite robust relationship with the one implied by the DEA
analysis. We also in terms of the DEA revisit topics like clustering,
mean-reversion and periodicities. We finally propose a GARCH inspired model but
for the price itself. Models in the context of stochastic volatility processes
appear under this scope to have a feasible description.Comment: 16 pages, 7 figure
AVOCADO: A Virtual Observatory Census to Address Dwarfs Origins
Dwarf galaxies are by far the most abundant of all galaxy types, yet their
properties are still poorly understood -especially due to the observational
challenge that their intrinsic faintness represents. AVOCADO aims at
establishing firm conclusions on their formation and evolution by constructing
a homogeneous, multiwavelength dataset for a statistically significant sample
of several thousand nearby dwarfs (-18 < Mi < -14). Using public data and
Virtual Observatory tools, we have built GALEX+SDSS+2MASS spectral energy
distributions that are fitted by a library of single stellar population models.
Star formation rates, stellar masses, ages and metallicities are further
complemented with structural parameters that can be used to classify them
morphologically. This unique dataset, coupled with a detailed characterization
of each dwar's environment, allows for a fully comprehensive investigation of
their origins and to track the (potential) evolutionary paths between the
different dwarf types.Comment: 4 pages, 1 figure. To appear in the proceedings of IAU Symposium 277,
"Tracing the Ancestry of Galaxies on the Land of our Ancestors", Carignan,
Freeman, and Combes, ed
Localized starbursts in dwarf galaxies produced by impact of low metallicity cosmic gas clouds
Models of galaxy formation predict that gas accretion from the cosmic web is
a primary driver of star formation over cosmic history. Except in very dense
environments where galaxy mergers are also important, model galaxies feed from
cold streams of gas from the web that penetrate their dark matter haloes.
Although these predictions are unambiguous, the observational support has been
indirect so far. Here we report spectroscopic evidence for this process in
extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of
localized starbursts associated with gas having low metallicity. Detailed
abundance analyses based on Gran Telescopio Canarias (GTC) optical spectra of
ten XMPs show that the galaxy hosts have metallicities around 60 % solar on
average, while the large star-forming regions that dominate their integrated
light have low metallicities of some 6 % solar. Because gas mixes azimuthally
in a rotation timescale (a few hundred Myr), the observed metallicity
inhomogeneities are only possible if the metal-poor gas fell onto the disk
recently. We analyze several possibilities for the origin of the metal-poor
gas, favoring the metal-poor gas infall predicted by numerical models. If this
interpretation is correct, XMPs trace the cosmic web gas in their surroundings,
making them probes to examine its properties.Comment: Accepted for publication in ApJ
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