1,073 research outputs found
Monte Carlo Hamiltonian - From Statistical Physics to Quantum Theory
Monte Carlo techniques have been widely employed in statistical physics as
well as in quantum theory in the Lagrangian formulation. However, in some areas
of application to quantum theories computational progress has been slow. Here
we present a recently developed approach: the Monte Carlo Hamiltonian method,
designed to overcome the difficulties of the conventional approach.Comment: StatPhys-Taiwan-1999, 6 pages, LaTeX using elsart.cl
Charge asymmetry in W + jets production at the LHC
The charge asymmetry in W + jets production at the LHC can serve to calibrate
the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n
jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying
particular attention to the uncertainty in the prediction from higher-order
perturbative corrections and uncertainties in parton distribution functions. We
show that these uncertainties are generally of order a few percent, making the
experimental measurement of the charge asymmetry ratio a particularly useful
diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex
Directed avalanche processes with underlying interface dynamics
We describe a directed avalanche model; a slowly unloading sandbox driven by
lowering a retaining wall. The directness of the dynamics allows us to
interpret the stable sand surfaces as world sheets of fluctuating interfaces in
one lower dimension. In our specific case, the interface growth dynamics
belongs to the Kardar-Parisi-Zhang (KPZ) universality class. We formulate
relations between the critical exponents of the various avalanche distributions
and those of the roughness of the growing interface. The nonlinear nature of
the underlying KPZ dynamics provides a nontrivial test of such generic exponent
relations. The numerical values of the avalanche exponents are close to the
conventional KPZ values, but differ sufficiently to warrant a detailed study of
whether avalanche correlated Monte Carlo sampling changes the scaling exponents
of KPZ interfaces. We demonstrate that the exponents remain unchanged, but that
the traces left on the surface by previous avalanches give rise to unusually
strong finite-size corrections to scaling. This type of slow convergence seems
intrinsic to avalanche dynamics.Comment: 13 pages, 13 figure
Resonance structures in the multichannel quantum defect theory for the photofragmentation processes involving one closed and many open channels
The transformation introduced by Giusti-Suzor and Fano and extended by
Lecomte and Ueda for the study of resonance structures in the multichannel
quantum defect theory (MQDT) is used to reformulate MQDT into the forms having
one-to-one correspondence with those in Fano's configuration mixing (CM) theory
of resonance for the photofragmentation processes involving one closed and many
open channels. The reformulation thus allows MQDT to have the full power of the
CM theory, still keeping its own strengths such as the fundamental description
of resonance phenomena without an assumption of the presence of a discrete
state as in CM.Comment: 7 page
Bilinear R-parity Violation and Small Neutrino Masses: a Self-consistent Framework
We study extensions of supersymmetric models without R-parity which include
an anomalous U(1)_H horizontal symmetry. Bilinear R-parity violating terms
induce a neutrino mass at tree level of approximately eV
where is the U(1)_H breaking parameter and is an
integer number that depends on the horizontal charges of the leptons. For
a unique self-consistent model arises in which i) all the
superpotential trilinear R-parity violating couplings are forbidden by
holomorphy; ii) the tree level neutrino mass falls in the range suggested by
the atmospheric neutrino problem; iii) radiative contributions to neutrino
masses are strongly suppressed resulting in a squared solar mass difference of
few 10^{-8} eV^2 which only allows for the LOW (or quasi-vacuum) solution to
the solar neutrino problem; iv) the neutrino mixing angles are not suppressed
by powers of and can naturally be large.Comment: Latex, 15 pages including 1 figure, some typos correcte
Neutrino Masses in the Supersymmetric Standard Model with Right-Handed Neutrinos and Spontaneous R-Parity Violation
We propose an extension of the supersymmetric standard model with
right-handed neutrinos and a singlet Higgs field, and study the neutrino masses
in this model. The Majorana masses for the right-handed neutrinos are generated
around the supersymmetry breaking scale through the vacuum expectation value of
the singlet Higgs field. This model may induce spontaneous R-parity violation
via the vacuum expectation value of the right-handed sneutrino. In the case,
the effective theory is similar to a bilinear R-parity violating model. There
are two sources for the neutrino masses: one is this bilinear R-parity breaking
effect, and the other is the ordinary seesaw effect between left- and
right-handed neutrinos. Combining these two effects, the hierarchical neutrino
mass pattern arises even when the neutrino Yukawa matrices are not
hierarchical. We acquire appropriate masses and mixings to explain both the
solar and atmospheric neutrino oscillations.Comment: 22pages, RevTeX, 3 ps figures; a reference adde
C-axis lattice dynamics in Bi-based cuprate superconductors
We present results of a systematic study of the c axis lattice dynamics in
single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer
Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both
experimental data obtained by spectral ellipsometry on single crystals and
theoretical calculations. The calculations are carried out within the framework
of a classical shell model, which includes long-range Coulomb interactions and
short-range interactions of the Buckingham form in a system of polarizable
ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and
Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes
of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve
good agreement between the calculated A2u eigenfrequencies and the experimental
values of the c axis TO phonon frequencies which allows us to make a reliable
phonon mode assignment for all three Bi-based cuprate superconductors. We also
present the results of our shell model calculations for the Gamma-point A1g
symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is
based on the published experimental Raman spectra. The
superconductivity-induced phonon anomalies recently observed in the c axis
infrared and resonant Raman scattering spectra in trilayer Bi2223 are
consistently explained with the suggested assignment.Comment: 29 pages, 13 figure
Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model
We extend the minimal supersymmetric standard model with bilinear R-parity
violation to include a pair of Higgs triplet superfields. The neutral
components of the Higgs triplets develop small vacuum expectation values (VEVs)
quadratic in the bilinear R-parity breaking parameters. In this scheme the
atmospheric neutrino mass scale arises from bilinear R-parity breaking while
for reasonable values of parameters the solar neutrino mass scale is generated
from the small Higgs triplet VEVs. We calculate neutrino masses and mixing
angles in this model and show how the model can be tested at future colliders.
The branching ratios of the doubly charged triplet decays are related to the
solar neutrino angle via a simple formula.Comment: 19 pages, 4 figures; one formula corrected, two author's names
corrected; some explanatory comments adde
Colloidal Quantum Dot Color Converters for Visible Light Communications
The properties and performance of CdSSe/ZnS colloidal quantum dot composite materials for use as InGaN LED color converters in visible light communications applications is reported. 500Mb/s optical wireless transmission is demonstrated
Charge asymmetry ratio as a probe of quark flavour couplings of resonant particles at the LHC
We show how a precise knowledge of parton distribution functions, in
particular those of the u and d quarks, can be used to constrain a certain
class of New Physics models in which new heavy charged resonances couple to
quarks and leptons. We illustrate the method by considering a left-right
symmetric model with a W' from a SU(2)_R gauge sector produced in
quark-antiquark annihilation and decaying into a charged lepton and a heavy
Majorana neutrino. We discuss a number of quark and lepton mixing scenarios,
and simulate both signals and backgrounds in order to determine the size of the
expected charge asymmetry. We show that various quark-W' mixing scenarios can
indeed be constrained by charge asymmetry measurements at the LHC, particularly
at 14 TeV centre of mass energy.Comment: 14 pages, 3 figure
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