623 research outputs found
Quantum Dynamics in Non-equilibrium Strongly Correlated Environments
We consider a quantum point contact between two Luttinger liquids coupled to
a mechanical system (oscillator). For non-vanishing bias, we find an effective
oscillator temperature that depends on the Luttinger parameter. A generalized
fluctuation-dissipation relation connects the decoherence and dissipation of
the oscillator to the current-voltage characteristics of the device. Via a
spectral representation, this result is generalized to arbitrary leads in a
weak tunneling regime.Comment: 4 pages, 1 figur
Hadronic Charmed Meson Decays Involving Axial Vector Mesons
Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an
axial-vector meson are studied. The charm to axial-vector meson transition form
factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole
momentum dependence of the transition form factor and the presence of
a sizable long-distance -exchange are the two key ingredients for
understanding the data of . The mixing angle of
the strange axial-vector mesons is found to be or
from decays. The study of decays excludes the positive mixing-angle
solutions. It is pointed out that an observation of the decay at the level of will rule out
and favor the solution .
Though the decays are color suppressed, they are
comparable to and even larger than the color-allowed counterparts: and . The finite width effect of the axial-vector resonance is
examined. It becomes important for in particular when its width is
near 600 MeV.Comment: 19 page
Superpotentials for M-theory on a G_2 holonomy manifold and Triality symmetry
For -theory on the holonomy manifold given by the cone on {\bf
S^3}\x {\bf S^3} we consider the superpotential generated by membrane
instantons and study its transformations properties, especially under monodromy
transformations and triality symmetry. We find that the latter symmetry is,
essentially, even a symmetry of the superpotential. As in Seiberg/Witten
theory, where a flat bundle given by the periods of an universal elliptic curve
over the -plane occurs, here a flat bundle related to the Heisenberg group
appears and the relevant universal object over the moduli space is related to
hyperbolic geometry.Comment: 58 pages, latex; references adde
Adiabatic Transfer of Electrons in Coupled Quantum Dots
We investigate the influence of dissipation on one- and two-qubit rotations
in coupled semiconductor quantum dots, using a (pseudo) spin-boson model with
adiabatically varying parameters. For weak dissipation, we solve a master
equation, compare with direct perturbation theory, and derive an expression for
the `fidelity loss' during a simple operation that adiabatically moves an
electron between two coupled dots. We discuss the possibility of visualizing
coherent quantum oscillations in electron `pump' currents, combining quantum
adiabaticity and Coulomb blockade. In two-qubit spin-swap operations where the
role of intermediate charge states has been discussed recently, we apply our
formalism to calculate the fidelity loss due to charge tunneling between two
dots.Comment: 13 pages, 8 figures, to appear in Phys. Rev.
Itinerant Ferromagnetism in the Periodic Anderson Model
We introduce a novel mechanism for itinerant ferromagnetism, based on a
simple two-band model. The model includes an uncorrelated and dispersive band
hybridized with a second band which is narrow and correlated. The simplest
Hamiltonian containing these ingredients is the Periodic Anderson Model (PAM).
Using quantum Monte Carlo and analytical methods, we show that the PAM and an
extension of it contain the new mechanism and exhibit a non-saturated
ferromagnetic ground state in the intermediate valence regime. We propose that
the mechanism, which does not assume an intra atomic Hund's coupling, is
present in both the iron group and in some f electron compounds like
Ce(Rh_{1-x} Ru_x)_3 B_2, La_x Ce_{1-x} Rh_3 B_2 and the uranium
monochalcogenides US, USe, and UTe
Efimov physics from the functional renormalization group
Few-body physics related to the Efimov effect is discussed using the
functional renormalization group method. After a short review of
renormalization in its modern formulation we apply this formalism to the
description of scattering and bound states in few-body systems of identical
bosons and distinguishable fermions with two and three components. The Efimov
effect leads to a limit cycle in the renormalization group flow. Recently
measured three-body loss rates in an ultracold Fermi gas Li atoms are
explained within this framework. We also discuss briefly the relation to the
many-body physics of the BCS-BEC crossover for two-component fermions and the
formation of a trion phase for the case of three species.Comment: 28 pages, 13 figures, invited contribution to a special issue of
"Few-Body Systems" devoted to Efimov physics, published versio
Efimov Trimers near the Zero-crossing of a Feshbach Resonance
Near a Feshbach resonance, the two-body scattering length can assume any
value. When it approaches zero, the next-order term given by the effective
range is known to diverge. We consider the question of whether this divergence
(and the vanishing of the scattering length) is accompanied by an anomalous
solution of the three-boson Schr\"odinger equation similar to the one found at
infinite scattering length by Efimov. Within a simple zero-range model, we find
no such solutions, and conclude that higher-order terms do not support Efimov
physics.Comment: 8 pages, no figures, final versio
Rotational master equation for cold laser-driven molecules
The equations of motion for the molecular rotation are derived for
vibrationally cold dimers that are polarized by off-resonant laser light. It is
shown that, by eliminating electronic and vibrational degrees of freedom, a
quantum master equation for the reduced rotational density operator can be
obtained. The coherent rotational dynamics is caused by stimulated Raman
transitions, whereas spontaneous Raman transitions lead to decoherence in the
motion of the quantized angular momentum. As an example the molecular dynamics
for the optical Kerr effect is chosen, revealing decoherence and heating of the
molecular rotation.Comment: 11 pages, 5 figures, to appear in Phys. Rev.
Search for lepton-flavor violation at HERA
A search for lepton-flavor-violating interactions and has been performed with the ZEUS detector using the entire HERA I
data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data
were taken at center-of-mass energies, , of 300 and 318 GeV. No
evidence of lepton-flavor violation was found, and constraints were derived on
leptoquarks (LQs) that could mediate such interactions. For LQ masses below
, limits were set on , where
is the coupling of the LQ to an electron and a
first-generation quark , and is the branching ratio of
the LQ to the final-state lepton ( or ) and a quark . For
LQ masses much larger than , limits were set on the four-fermion
interaction term for LQs that couple to an electron and a quark
and to a lepton and a quark , where and are
quark generation indices. Some of the limits are also applicable to
lepton-flavor-violating processes mediated by squarks in -Parity-violating
supersymmetric models. In some cases, especially when a higher-generation quark
is involved and for the process , the ZEUS limits are the most
stringent to date.Comment: 37 pages, 10 figures, Accepted by EPJC. References and 1 figure (Fig.
6) adde
Multijet production in neutral current deep inelastic scattering at HERA and determination of alpha_s
Multijet production rates in neutral current deep inelastic scattering have
been measured in the range of exchanged boson virtualities 10 < Q2 < 5000 GeV2.
The data were taken at the ep collider HERA with centre-of-mass energy sqrt(s)
= 318 GeV using the ZEUS detector and correspond to an integrated luminosity of
82.2 pb-1. Jets were identified in the Breit frame using the k_T cluster
algorithm in the longitudinally invariant inclusive mode. Measurements of
differential dijet and trijet cross sections are presented as functions of jet
transverse energy E_{T,B}{jet}, pseudorapidity eta_{LAB}{jet} and Q2 with
E_{T,B}{jet} > 5 GeV and -1 < eta_{LAB}{jet} < 2.5. Next-to-leading-order QCD
calculations describe the data well. The value of the strong coupling constant
alpha_s(M_Z), determined from the ratio of the trijet to dijet cross sections,
is alpha_s(M_Z) = 0.1179 pm 0.0013(stat.) {+0.0028}_{-0.0046}(exp.)
{+0.0064}_{-0.0046}(th.)Comment: 22 pages, 5 figure
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