9,265 research outputs found
Dynamical Symmetry Breaking With a Fourth Generation
Adding a fourth generation to the Standard Model and assuming it to be valid
up to some cutoff \Lambda, we show that electroweak symmetry is broken by
radiative corrections due to the fourth generation. The effects of the fourth
generation are isolated using a Lagrangian with a genuine scalar without
self-interactions at the classical level. For masses of the fourth generation
consistent with electroweak precision data (including the B \rightarrow K \pi\
CP asymmetries) we obtain a Higgs mass of the order of a few hundreds GeV and a
cutoff \Lambda\ around 1-2 TeV. We study the reliability of the perturbative
treatment used to obtain these results taking into account the running of the
Yukawa couplings of the fourth quark generation with the aid of the
Renormalization Group (RG) equations, finding similar allowed values for the
Higgs mass but a slightly lower cut-off due to the breaking of the perturbative
regime. Such low cut-off means that the effects of new physics needed to
describe electroweak interactions at energy above \Lambda\ should be measurable
at the LHC. We use the minimal supersymmetric extension of the standard model
with four generations as an explicit example of models realizing the dynamical
electroweak symmetry breaking by radiative corrections and containing new
physics. Here, the cutoff is replaced by the masses of the squarks and
electroweak symmetry breaking by radiative corrections requires the squark
masses to be of the order of 1 TeV.Comment: 20 pages, 7 figures. New section adde
Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates
In this study we investigate magnetic properties, surface morphology and
crystal structure in iron nanoclusters electrodeposited on lightly-doped (100)
n-type silicon substrates. Our goal is to investigate the spin injection and
detection in the Fe/Si lateral structures. The samples obtained under electric
percolation were characterized by magnetoresistive and magnetic resonance
measurements with cycling the sweeping applied field in order to understand the
spin dynamics in the as-produced samples. The observed hysteresis in the
magnetic resonance spectra, plus the presence of a broad peak in the
non-saturated regime confirming the low field microwave absorption (LFMA), were
correlated to the peaks and slopes found in the magnetoresistance curves. The
results suggest long range spin injection and detection in low resistive
silicon and the magnetic resonance technique is herein introduced as a
promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure
Interação genótipo x ambiente para produção de leite na raça Pardo SuÃço, utilizando-se inferência Bayesiana.
Informações de 2.981 lactações referentes à s primeiras lactações de vacas da raça Pardo-SuÃça, filhas de 151 reprodutores, distribuÃdas em 62 rebanhos, com parições entre 1980 a 2002, foram utilizadas para se verificar a existência da heterogeneidade de variância entre rebanhos e o seu impacto na classificação de reprodutores. As produções de leite foram utilizadas para se classificar os rebanhos em nÃveis de alta e baixa produção. Utilizou-se um modelo animal que incluiu os efeitos fixos de rebanho-ano e estação de parto, efeito linear do perÃodo de lactação, linear e quadrático da idade da vaca ao parto, como covariáveis, além dos efeitos aleatórios de animal e ambiente temporário. Estimaram-se componentes de variância, considerando-se os rebanhos como uma única amostra e assumindo-se a produção de leite em cada nÃvel de produção como caracterÃstica diferente. Médias e componentes de variância foram maiores para o nÃvel de alta produção, caracterizando a presença de heterogeneidade de variância entre os rebanhos. As estimativas de herdabilidade foram de 0,21 em ambos os nÃveis para a produção de leite e de 0,25 e 0,26 para os nÃveis de alta e baixa produção, respectivamente. As correlações genéticas entre os nÃveis foram de 0,48, indicando a presença de heterogeneidade de variâncias. Correlações de Spearman entre os valores genéticos dos reprodutores preditos em análise conjunta com o nÃvel de alta produção foram altas, enquanto que correlações baixas foram observadas para o nÃvel de produção baixo, para os 10, 20 e 30% dos melhores reprodutores. Reprodutores com proles em rebanhos mais variáveis estariam sendo melhores classificados na avaliação genética, quando se desconsidera a heterogeneidade de variânci
On Field Induced Diaelastic Effect in a Small Josephson Contact
An analog of the diaelastic effect is predicted to occur in a small Josephson
contact with Josephson vortices manifesting itself as magnetic field induced
softening of the contact shear modulus C(T,H). In addition to Fraunhofer type
field oscillations, C(T,H) is found to exhibit pronounced flux driven
temperature oscillations near T_C
Discovery of 15-second oscillations in Hubble Space Telescope observations of WZ Sagittae following the 2001 outburst
We report the discovery of 15-s oscillations in ultraviolet observations of
WZ Sge obtained with the Hubble Space Telescope approximately one month after
the peak of the 2001 outburst. This is the earliest detection of oscillations
in WZ Sge following an outburst and the first time that a signal near 15 s has
been seen to be dominant. The oscillations are quite strong (amplitude about
5%), but not particularly coherent. In one instance, the oscillation period
changed by 0.7 s between successive observations separated by less than 1 hour.
We have also found evidence for weaker signals with periods near 6.5 s in some
of our data. We discuss the implications of our results for the models that
have been proposed to account for the 28-s oscillations seen in quiescence. If
the periods of the 15-s oscillations can be identified with the periods of
revolution of material rotating about the white dwarf, the mass of the white
dwarf must satisfy M_WD > 0.71 M_sun. The corresponding limit for the 6.5-s
signals is M_WD > 1.03 M_sun.Comment: accepted for publication in ApJ Letters; 13 pages, 4 postscript
figures; new version corrects a few typos and matches version that will
appear in ApJ
A Possible Dynamical Effect of a Primordial Magnetic Field
The possible existence of a primordial magnetic field in the universe has
been previously investigated in many articles. Studies involving the influence
of a magnetic field in the nucleosyntesis era, studies considering the effects
in the formation of structures during the radiation era and the matter era have
been considered. We here assume the existence of a primordial magnetic field
and study its effect, in particular, in the formation of voids. The study is
twofold: to put constraints on the strength of the magnetic field during the
recombination era and to preview its effects on the formation of voids.Comment: 21 pages, aasms4.sty AAS Latex V4.0 file, 3 EPS figures included.
Also available at http://www.iagusp.usp.br/ To appear in the Ap
Experimental and theoretical evidences for the ice regime in planar artificial spin ices
In this work, we explore a kind of geometrical effect in the thermodynamics
of artificial spin ices (ASI). In general, such artificial materials are
athermal. Here, We demonstrate that geometrically driven dynamics in ASI can
open up the panorama of exploring distinct ground states and thermally magnetic
monopole excitations. It is shown that a particular ASI lattice will provide a
richer thermodynamics with nanomagnet spins experiencing less restriction to
flip precisely in a kind of rhombic lattice. This can be observed by analysis
of only three types of rectangular artificial spin ices (RASI). Denoting the
horizontal and vertical lattice spacings by a and b, respectively, then, a RASI
material can be described by its aspect ratio =a/b. The rhombic lattice
emerges when =. So, by comparing the impact of thermal
effects on the spin flips in these three appropriate different RASI arrays, it
is possible to find a system very close to the ice regime
Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator Films at Room Temperature
We report the spin to charge current conversation in an intrinsic topological
insulator (TI) film at room temperature. The spin
currents are generated in a thin layer of permalloy (Py) by two different
processes, spin pumping (SPE) and spin Seebeck effects (SSE). In the first we
use microwave-driven ferromagnetic resonance of the Py film to generate a SPE
spin current that is injected into the TI layer in
direct contact with Py. In the second we use the SSE in the longitudinal
configuration in Py without contamination by the Nernst effect made possible
with a thin NiO layer between the Py and layers.
The spin-to-charge current conversion is attributed to the inverse Edelstein
effect (IEE) made possible by the spin-momentum locking in the electron Fermi
contours due to the Rashba field. The measurements by the two techniques yield
very similar values for the IEE parameter, which are larger than the reported
values in the previous studies on topological insulators.Comment: 18 pages and 7 figure
- …