840 research outputs found
Fixed boundary conditions analysis of the 3d Gonihedric Ising model with
The Gonihedric Ising model is a particular case of the class of models
defined by Savvidy and Wegner intended as discrete versions of string theories
on cubic lattices. In this paper we perform a high statistics analysis of the
phase transition exhibited by the 3d Gonihedric Ising model with in the
light of a set of recently stated scaling laws applicable to first order phase
transitions with fixed boundary conditions. Even though qualitative evidence
was presented in a previous paper to support the existence of a first order
phase transition at , only now are we capable of pinpointing the
transition inverse temperature at and of checking the
scaling of standard observables.Comment: 14 pages, 5 tables, 2 figures, uses elsart.cls packag
Production and decays of supersymmetric Higgs bosons in spontaneously broken R-parity
We study the mass spectra, production and decay properties of the lightest
supersymmetric CP-even and CP-odd Higgs bosons in models with spontaneously
broken R-parity (SBRP). We compare the resulting mass spectra with expectations
of the Minimal Supersymmetric Standard Model (MSSM), stressing that the model
obeys the upper bound on the lightest CP-even Higgs boson mass. We discuss how
the presence of the additional scalar singlet states affects the Higgs
production cross sections, both for the Bjorken process and the "associated
production". The main phenomenological novelty with respect to the MSSM comes
from the fact that the spontaneous breaking of lepton number leads to the
existence of the majoron, denoted J, which opens new decay channels for
supersymmetric Higgs bosons. We find that the invisible decays of CP-even
Higgses can be dominant, while those of the CP-odd bosons may also be sizeable.Comment: 21 pages, 8 figures; minor changes, final version for publicatio
Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. III. Abundances and Velocities for a Sample of 14 Clusters
We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters
in the region of the CaII lines with FORS2 on the Very Large Telescope (VLT).
We determined the mean metallicity and radial velocity with mean errors of 0.05
dex and 2.6 km/s, respectively, from a mean of 6.5 members per cluster. One
cluster (B113) was too young for a reliable metallicity determination and was
excluded from the sample. We combined the sample studied here with 15 clusters
previously studied by us using the same technique, and with 7 clusters whose
metallicities determined by other authors are on a scale similar to ours. This
compilation of 36 clusters is the largest SMC cluster sample currently
available with accurate and homogeneously determined metallicities. We found a
high probability that the metallicity distribution is bimodal, with potential
peaks at -1.1 and -0.8 dex. Our data show no strong evidence of a metallicity
gradient in the SMC clusters, somewhat at odds with recent evidence from CaT
spectra of a large sample of field stars Dobbie et al. (2014). This may be
revealing possible differences in the chemical history of clusters and field
stars. Our clusters show a significant dispersion of metallicities, whatever
age is considered, which could be reflecting the lack of a unique AMR in this
galaxy. None of the chemical evolution models currently available in the
literature satisfactorily represents the global chemical enrichment processes
of SMC clusters.Comment: 49 pages, 15 figures. Accepted for publication in A
Degenerate neutrinos from a supersymmetric A_4 model
We investigate the supersymmetric A_4 model recently proposed by Babu, Ma and
Valle. The model naturally gives quasi-degenerate neutrinos that are bi-largely
mixed, in agreement with observations. Furthermore, the mixings in the quark
sector are constrained to be small, making it a complete model of the flavor
structure. Moreover, it has the interesting property that CP-violation in the
leptonic sector is maximal (unless vanishing). The model exhibit a close
relation between the slepton and lepton sectors and we derive the slepton
spectra that are compatible with neutrino data and the present bounds on
flavor-violating charged lepton decays. The prediction for the branching ratio
of the decay tau -> mu gamma has a lower limit of 10^{-9}. In addition, the
overall neutrino mass scale is constrained to be larger than 0.3 eV. Thus, the
model will be tested in the very near future.Comment: 11 pages, 6 figures. Talk given at the International Workshop on
Astroparticle and High Energy Physics (AHEP), Valencia, Spain, 14-18 Oct.
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Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. IV. ABUNDANCES FOR A LARGE SAMPLE OF FIELD STARS AND COMPARISON WITH THE CLUSTER SAMPLE
This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7 km s-1 and 0.16 dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4\ub0, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions
Non-equilibrium melting of colloidal crystals in confinement
We report on a novel and flexible experiment to investigate the
non-equilibrium melting behaviour of model crystals made from charged colloidal
spheres. In a slit geometry polycrystalline material formed in a low salt
region is driven by hydrostatic pressure up an evolving gradient in salt
concentration and melts at large salt concentration. Depending on particle and
initial salt concentration, driving velocity and the local salt concentration
complex morphologic evolution is observed. Crystal-melt interface positions and
the melting velocity are obtained quantitatively from time resolved Bragg- and
polarization microscopic measurements. A simple theoretical model predicts the
interface to first advance, then for balanced drift and melting velocities to
become stationary at a salt concentration larger than the equilibrium melting
concentration. It also describes the relaxation of the interface to its
equilibrium position in a stationary gradient after stopping the drive in
different manners. We further discuss the influence of the gradient strength on
the resulting interface morphology and a shear induced morphologic transition
from polycrystalline to oriented single crystalline material before melting
Minimal supergravity radiative effects on the tri-bimaximal neutrino mixing pattern
We study the stability of the Harrison-Perkins-Scott (HPS) mixing pattern,
assumed to hold at some high energy scale, against supersymmetric radiative
corrections. We work in the framework of a reference minimal supergravity model
(mSUGRA) where supersymmetry breaking is universal and flavor-blind at
unification. The radiative corrections considered include both RGE running as
well as threshold effects. We find that in this case the solar mixing angle can
only increase with respect to the HPS reference value, while the atmospheric
and reactor mixing angles remain essentially stable. Deviations from the solar
angle HPS prediction towards lower values would signal novel contributions from
physics beyond the simplest mSUGRA model.Comment: 13 pages, 3 figures; added reference; final version for publicatio
Predicting Neutrinoless Double Beta Decay
We give predictions for the neutrinoless double beta decay rate in a simple
variant of the A_4 family symmetry model. We show that there is a lower bound
for the neutrinoless double beta decay amplitude even in the case of normal
hierarchical neutrino masses, corresponding to an effective mass parameter
|m_{ee}| >= 0.17 \sqrt{\Delta m^2_{ATM}}. This result holds both for the CP
conserving and CP violating cases. In the latter case we show explicitly that
the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We
conclude therefore that in our scheme, neutrinoless double beta decay may be
accessible to the next generation of high sensitivity experiments.Comment: 4 pages, 5 figures, 1 tabl
Invisible Higgs Boson Decays in Spontaneously Broken R-Parity
The Higgs boson may decay mainly to an invisible mode characterized by
missing energy, instead of the Standard Model channels. This is a generic
feature of many models where neutrino masses arise from the spontaneous
breaking of ungauged lepton number at relatively low scales, such as
spontaneously broken R-parity models. Taking these models as framework, we
reanalyze this striking suggestion in view of the recent data on neutrino
oscillations that indicate non-zero neutrino masses. We show that, despite the
smallness of neutrino masses, the Higgs boson can decay mainly to the invisible
Goldstone boson associated to the spontaneous breaking of lepton number. This
requires a gauge singlet superfield coupling to the electroweak doublet
Higgses, as in the Next to Minimal Supersymmetric Standard Model (NMSSM)
scenario for solving the -problem. The search for invisibly decaying Higgs
bosons should be taken into account in the planning of future accelerators,
such as the Large Hadron Collider and the Next Linear Collider.Comment: 24 pages, 10 figures; typos corrected, published versio
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