1,228 research outputs found
Crossing the phantom divide without phantom matter
A class of braneworld models can lead to phantom-like acceleration of the late universe, but without the need for any phantom matter. In the simplest models, the universe contains only cold dark matter and a cosmological constant. We generalize these models by introducing a quintessence field. The new feature in our models is that quintessence leads to a crossing of the phantom divide, . This is a purely gravitational effect, and there is no phantom instability. Furthermore, the Hubble parameter is always decreasing, and there is no big rip singularity in the future
Refining the predictions of supersymmetric CP-violating models: A top-down approach
We explore in detail the consequences of the CP-violating phases residing in
the supersymmetric and soft SUSY breaking parameters in the approximation that
family flavour mixings are ignored. We allow for non-universal boundary
conditions and in such a consideration the model is described by twelve
independent CP-violating phases and one angle which misaligns the vacuum
expectation values (VEVs) of the Higgs scalars. We run two-loop renormalization
group equations (RGEs), for all parameters involved, including phases, and we
properly treat the minimization conditions using the one-loop effective
potential with CP-violating phases included. We show that the two-loop running
of phases may induce sizable effects for the electric dipole moments (EDMs)
that are absent in the one-loop RGE analysis. Also important corrections to the
EDMs are induced by the Higgs VEVs misalignment angle which are sizable in the
large tanb region. Scanning the available parameter space we seek regions
compatible with accelerator and cosmological data with emphasis on rapid
neutralino annihilations through a Higgs resonance. It is shown that large
CP-violating phases, as required in Baryogenesis scenarios, can be tuned to
obtain agreement with WMAP3 cold dark matter constraints, EDMs and all
available accelerator data, in extended regions of the parameter space which
may be accessible to LHC.Comment: 41 pages, 22 eps figures. A reference added and a typo corrected;
version to appear in JHE
One-loop Higgs mass finiteness in supersymmetric Kaluza-Klein theories
We analyze the one-loop ultraviolet sensitivity of the Higgs mass in a
five-dimensional supersymmetric theory compactified on the orbifold S^1/Z_2,
with superpotential localized on a fixed-point brane. Four-dimensional
supersymmetry is broken by Scherk-Schwarz boundary conditions. Kaluza-Klein
interactions are regularized by means of a brane Gaussian distribution along
the extra dimension with length l_s\simeq\Lambda^{-1}_s, where \Lambda_s is the
cutoff of the five-dimensional theory. The coupling of the n-mode, with mass
M^{(n)}, acquires the n-dependent factor exp{-(M^{(n)}/\Lambda_s)^2/2}, which
makes it to decouple for M^{(n)}\gg \Lambda_s. The sensitivity of the Higgs
mass on \Lambda_s is strongly suppressed and quadratic divergences cancel by
supersymmetry. The one-loop correction to the Higgs mass is finite and equals,
for large values of \Lambda_s, the value obtained by the so-called
KK-regularization.Comment: 8 pages, 1 figure. The discussion on the distribution giving rise to
couplings suppressed by exp(-M/Lambda) is revised and the result is finite
and equals that of the Gaussian cas
Accurate quantitative EDS-TEM analysis of precipitates and matrix in equilibrium (α+β) Zr–1Nb alloys with Ta addition
The (α+β) phase microstructure in Zr-1.05Nb, Zr-0.85Nb-0.20Ta and Zr-0.85Nb-0.40Ta (wt.%) alloys annealed at 570 °C for 3840 h after β-quenching were observed at different scales by optical, SEM and TEM microscopies. A quantitative study of phase chemical compositions was carried out by EDS-TEM with experimental Cliff-Lorimer factors. The α matrix was measured on thin films and the β particle on carbon extractive replicas. The Ta addition showed a continuous increase of (Nb + Ta) solubility in α-Zr and (Zr + Ta) solubility in the β-Nb phase. The increase of Ta in the nominal composition of the Zr-1(Nb, Ta) alloy causes the decrease of the mass fraction of β-Nb phase.Fil: Ferreirós, Pedro Antonio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Universidad Tecnológica Nacional. Facultad Regional Haedo; ArgentinaFil: Alonso, P. R.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Quirós, D. P.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); ArgentinaFil: Zelaya, E.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Rubiolo, Gerardo Hector. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentin
Crystalline Structure and Vacancy Ordering across a Surface Phase Transition in Sn/Cu(001)
We report a surface X-ray diffraction study of the crystalline structure changes and critical behavior across the (3√2 × √2)R45° → (√2 × √2)R45° surface phase transition at 360 K for 0.5 monolayers of Sn on Cu(100). The phase transition is of the order-disorder type and is due to the disordering of the Cu atomic vacancies present in the low temperature phase. Two different atomic sites for Sn atoms, characterized by two different heights, are maintained across the surface phase transition.This work was funded by the Spanish MINECO under Grants FIS2011-23230 and MAT2014-52477-C5-5-P. E.G.M. and P.S. acknowledge financial support from MINECO through the “Maria de Maeztu” Programme for Units of Excellence in R&D (MDM-2014-0377).Peer Reviewe
Phenomenology of the nMSSM from colliders to cosmology
Low energy supersymmetric models provide a solution to the hierarchy problem
and also have the necessary ingredients to solve two of the most outstanding
issues in cosmology: the origin of dark matter and baryonic matter. One of the
most attractive features of this framework is that the relevant physical
processes are related to interactions at the weak scale and therefore may be
tested in collider experiments in the near future. This is true for the Minimal
Supersymmetric Standard Model (MSSM) as well as for its extension with the
addition of one singlet chiral superfield, the so-called nMSSM. It has been
recently shown that within the nMSSM an elegant solution to both the problem of
baryogenesis and dark matter may be found, that relies mostly on the mixing of
the singlet sector with the Higgs sector of the theory. In this work we review
the nMSSM model constraints from cosmology and present the associated collider
phenomenology at the LHC and the ILC. We show that the ILC will efficiently
probe the neutralino, chargino and Higgs sectors, allowing to confront
cosmological observations with computations based on collider measurements. We
also investigate the prospects for a direct detection of dark matter and the
constraints imposed by the current bounds of the electron electric dipole
moment in this model.Comment: 44 pp, 10 figures; Fig.9 replaced; discussion on CP violation
extended and references added; few minor additions in text about details of
the cut
CP violation in the secluded U(1)'-extended MSSM
We study the Higgs sector of the secluded -extended MSSM (sMSSM)
focusing on CP violation. Using the one-loop effective potential that includes
contributions from quarks and squarks in the third generation, we search for
the allowed region under theoretical and experimental constraints. It is found
that the possible region for the electroweak vacuum to exist is quite limited,
depending on the parameters in the model. The masses and couplings of the Higgs
bosons are calculated with/without CP violation. Even at the tree level, CP
violation is possible by complex soft SUSY breaking masses. Similar to the CPX
scenario in the MSSM, the scalar-pseudoscalar mixing enables the lightest Higgs
boson mass to become smaller than the boson mass while the coupling with
the boson is sufficiently suppressed to avoid the LEP experimental
constraints. However, unlike the CPX scenario, large and are not
required for the realization of large CP violation. The typical spectrum of the
SUSY particles is thus different. We also investigate the possible upper bound
of the lightest Higgs boson in the case of spontaneous CP violation. The
maximal value of it can reach above 100 GeV with maximal CP-violating phases.Comment: 28 pages, 16 figures, JHEP styl
Antiprotozoal activity of natural products from Nigerien plants used in folk medicine
In the course of the screening of plants from Niger for antiprotozoal activity, the methanol extract of Cassia sieberiana, and the dichloromethane extracts of Ziziphus mauritiana and Sesamun alatum were found to be active against protozoan parasites, namely Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and/or Plasmodium falciparum. Myricitrin (1), quercitrin (2) and 1-palmitoyl-lysolecithin (3) were isolated from C. sieberiana. From Z. mauritiana, the three triterpene derivatives 13, 15, and 16 are described here for the first time. Their chemical structures were determined by 1D and 2D NMR experiments, UV, IR and HRESIMS data. The absolute configurations were assigned via comparison of the experimental and calculated ECD spectra. In addition, eight known cyclopeptide alkaloids (4, 5, 7-12), and five known triterpenoids (6, 14, 17-19) were isolated. The antiprotozoal activity of the isolated compounds, as well as of eleven quinone derivatives (20-30) previously isolated from S. alatum was determined in vitro. The cytotoxicity in L6 rat myoblast cells was also evaluated. Compound 18 showed the highest antiplasmodial activity (IC(50) = 0.2 microm) and compound 24 inhibited T. b. rhodesiense with an IC(50) value of 0.007 microM. However, it also displayed significant cytotoxicity in L6 cells (IC(50) = 0.4 microm)
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