5,825 research outputs found
Production of doubly charged scalars from the decay of singly charged scalars in the Higgs Triplet Model
The existence of doubly charged Higgs bosons (H^{\pm\pm}) is a distinctive
feature of the Higgs Triplet Model (HTM), in which neutrinos obtain tree-level
masses from the vacuum expectation value of a neutral scalar in a triplet
representation of SU(2)_L. We point out that a large branching ratio for the
decay of a singly charged Higgs boson to a doubly charged Higgs boson via
H^\pm\to H^{\pm\pm}W^* is possible in a sizeable parameter space of the HTM.
From the production mechanism q'qbar\to W^* \to H^{\pm\pm}H^\mp the above decay
mode would give rise to pair production of H^{\pm\pm}, with a cross section
which can be comparable to that of the standard pair-production mechanism
qqbar\to \gamma^*,Z^* \to H^{++}H^{--}. We suggest that the presence of a
sizeable branching ratio for H^\pm\to H^{\pm\pm}W^* could significantly enhance
the detection prospects of H^{\pm\pm} in the four-lepton channel. Moreover, the
decays H^0\to H^\pm W^* and A^0\to H^\pm W^* from production of the neutral
triplet scalars H^0 and A^0 would also provide an additional source of H^\pm,
which can subsequently decay to H^{\pm\pm}.Comment: 13 pages, 3 figures, two figures added in v2, to appear in Physical
Review
Quantum Monte Carlo study of confined fermions in one-dimensional optical lattices
Using quantum Monte Carlo (QMC) simulations we study the ground-state
properties of the one-dimensional fermionic Hubbard model in traps with an
underlying lattice. Since due to the confining potential the density is space
dependent, Mott-insulating domains always coexist with metallic regions, such
that global quantities are not appropriate to describe the system. We define a
local compressibility that characterizes the Mott-insulating regions and
analyze other local quantities. It is shown that the momentum distribution
function, a quantity that is commonly considered in experiments, fails in
giving a clear signal of the Mott-insulator transition. Furthermore, we analyze
a mean-field approach to these systems and compare it with the numerically
exact QMC results. Finally, we determine a generic form for the phase diagram
that allows us to predict the phases to be observed in the experiments.Comment: RevTex file, 13 pages, 19 figures, published versio
Non-Oberbeck-Boussinesq effects in two-dimensional Rayleigh-Benard convection in glycerol
We numerically analyze Non-Oberbeck-Boussinesq (NOB) effects in
two-dimensional Rayleigh-Benard flow in glycerol, which shows a dramatic change
in the viscosity with temperature. The results are presented both as functions
of the Rayleigh number (Ra) up to (for fixed temperature difference
between the top and bottom plates) and as functions of
"non-Oberbeck-Boussinesqness'' or "NOBness'' () up to 50 K (for fixed
Ra). For this large NOBness the center temperature is more than 5 K
larger than the arithmetic mean temperature between top and bottom plate
and only weakly depends on Ra. To physically account for the NOB deviations of
the Nusselt numbers from its Oberbeck-Boussinesq values, we apply the
decomposition of into the product of two effects, namely
first the change in the sum of the top and bottom thermal BL thicknesses, and
second the shift of the center temperature as compared to . While
for water the origin of the deviation is totally dominated by the second
effect (cf. Ahlers et al., J. Fluid Mech. 569, pp. 409 (2006)) for glycerol the
first effect is dominating, in spite of the large increase of as compared
to .Comment: 6 pages, 7 figure
The Degrees of Freedom of Partial Least Squares Regression
The derivation of statistical properties for Partial Least Squares regression
can be a challenging task. The reason is that the construction of latent
components from the predictor variables also depends on the response variable.
While this typically leads to good performance and interpretable models in
practice, it makes the statistical analysis more involved. In this work, we
study the intrinsic complexity of Partial Least Squares Regression. Our
contribution is an unbiased estimate of its Degrees of Freedom. It is defined
as the trace of the first derivative of the fitted values, seen as a function
of the response. We establish two equivalent representations that rely on the
close connection of Partial Least Squares to matrix decompositions and Krylov
subspace techniques. We show that the Degrees of Freedom depend on the
collinearity of the predictor variables: The lower the collinearity is, the
higher the Degrees of Freedom are. In particular, they are typically higher
than the naive approach that defines the Degrees of Freedom as the number of
components. Further, we illustrate how the Degrees of Freedom approach can be
used for the comparison of different regression methods. In the experimental
section, we show that our Degrees of Freedom estimate in combination with
information criteria is useful for model selection.Comment: to appear in the Journal of the American Statistical Associatio
Systematic limits on sin^2{2theta_{13}} in neutrino oscillation experiments with multi-reactors
Sensitivities to sin^2{2theta_{13}} without statistical errors (``systematic
limit'') are investigated in neutrino oscillation experiments with multiple
reactors. Using an analytical approach, we show that the systematic limit on
sin^2{2theta_{13}} is dominated by the uncorrelated systematic error sigma_u of
the detector. Even in an experiment with multi-detectors and multi-reactors, it
turns out that most of the systematic errors including the one due to the
nature of multiple sources is canceled as in the case with a single reactor
plus two detectors, if the near detectors are placed suitably. The case of the
KASKA plan (7 reactors and 3 detectors) is investigated in detail, and it is
explicitly shown that it does not suffer from the extra uncertainty due to
multiple reactors.Comment: 26 pages, 10 eps-files, revtex
Cosmological-Constant Cold Dark Matter Models and the COBE Two-Year Sky maps
We compare the two-year COBE DMR sky maps with the predictions of
cosmological-constant cold dark matter models. Using a Bayesian analysis, we
find that the most likely value of the cosmological constant in such a model is
Lambda = 0. The data set an upper limit on Lambda of 0.78 (0.85) at 90%
confidence, and 0.86 (0.92) at 95% confidence with (without) the quadrupole
anisotropy.Comment: 10 pages + 3 figures of uuencoded compressed PostScript. Preprint
number CfPA-94-th-33, UTAP-187. (We have corrected an error in our analysis.
Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory
We develop a projective quantum Monte Carlo algorithm of the Hirsch-Fye type
for obtaining ground state properties of the Anderson impurity model. This
method is employed to solve the self-consistency equations of dynamical mean
field theory. It is shown that the approach converges rapidly to the ground
state so that reliable zero-temperature results are obtained. As a first
application, we study the Mott-Hubbard metal-insulator transition of the
one-band Hubbard model, reconfirming the numerical renormalization group
results.Comment: 4 pages, 4 figure
Mean Field Phase Diagram of SU(2)xSU(2) Lattice Higgs-Yukawa Model at Finite Lambda
The phase diagram of an SU(2)_L x SU(2)_R lattice Higgs-Yukawa model with
finite lambda is constructed using mean field theory. The phase diagram bears a
superficial resemblance to that for infinite lambda, however as lambda is
decreased the paramagnetic region shrinks in size. For small lambda the phase
transitions remain second order, and no new first order transitions are seen.Comment: 9 pages, 3 postscript figures, RevTex. To appear in PR
Time-dependent density functional theory for strong electromagnetic fields in crystalline solids
We apply the coupled dynamics of time-dependent density functional theory and
Maxwell equations to the interaction of intense laser pulses with crystalline
silicon. As a function of electromagnetic field intensity, we see several
regions in the response. At the lowest intensities, the pulse is reflected and
transmitted in accord with the dielectric response, and the characteristics of
the energy deposition is consistent with two-photon absorption. The absorption
process begins to deviate from that at laser intensities ~ 10^13 W/cm^2, where
the energy deposited is of the order of 1 eV per atom. Changes in the
reflectivity are seen as a function of intensity. When it passes a threshold of
about 3 \times 1012 W/cm2, there is a small decrease. At higher intensities,
above 2 \times 10^13 W/cm^2, the reflectivity increases strongly. This behavior
can be understood qualitatively in a model treating the excited electron-hole
pairs as a plasma.Comment: 27 pages; 11 figure
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