13,195 research outputs found

### Super and Sub-Poissonian photon statistics for single molecule spectroscopy

We investigate the distribution of the number of photons emitted by a single
molecule undergoing a spectral diffusion process and interacting with a
continuous wave laser field. The spectral diffusion is modeled based on a
stochastic approach, in the spirit of the Anderson-Kubo line shape theory.
Using a generating function formalism we solve the generalized optical Bloch
equations, and obtain an exact analytical formula for the line shape and
Mandel's Q parameter. The line shape exhibits well known behaviors, including
motional narrowing when the stochastic modulation is fast, and power
broadening. The Mandel parameter, describing the line shape fluctuations,
exhibits a transition from a Quantum sub-Poissonian behavior in the fast
modulation limit, to a classical super-Poissonian behavior found in the slow
modulation limit. Our result is applicable for weak and strong laser field,
namely for arbitrary Rabi frequency. We show how to choose the Rabi frequency
in such a way that the Quantum sub-Poissonian nature of the emission process
becomes strongest. A lower bound on $Q$ is found, and simple limiting behaviors
are investigated. A non-trivial behavior is obtained in the intermediate
modulation limit, when the time scales for spectral diffusion and the life time
of the excited state, become similar. A comparison is made between our results,
and previous ones derived based on the semi-classical generalized
Wiener--Khintchine theorem.Comment: 14 Phys. Rev style pages, 10 figure

### Gravitational Waves from First-Order Phase Transitions: LIGO as a Window to Unexplored Seesaw Scales

Within a recently proposed classically conformal model, in which the
generation of neutrino masses is linked to spontaneous scale symmetry breaking,
we investigate the associated phase transition and find it to be of strong
first order with a substantial amount of supercooling. Carefully taking into
account the vacuum energy of the metastable minimum, we demonstrate that a
significant fraction of the model's parameter space can be excluded simply
because the phase transition cannot complete. We argue this to be a powerful
consistency check applicable to general theories based on classical scale
invariance. Finally, we show that all remaining parameter points predict a
sizable gravitational wave signal, so that the model can be fully tested by
future gravitational wave observatories. In particular, most of the parameter
space can already be probed by the upcoming LIGO science run starting in early
2019.Comment: 16 pages, 6 figures; calculation of signal-to-noise ratio updated,
references adde

### Fourier's Law from Schroedinger Dynamics

We consider a class of one-dimensional chains of weakly coupled many level
systems. We present a theory which predicts energy diffusion within these
chains for almost all initial states, if some concrete conditions on their
Hamiltonians are met. By numerically solving the time dependent Schroedinger
equation, we verify this prediction. Close to equilibrium we analyze this
behavior in terms of heat conduction and compute the respective coefficient
directly from the theory.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

### Electronic structure and resistivity of the double exchange model

The double exchange (DE) model with quantum local spins S is studied; an
equation of motion approach is used and decoupling approximations analogous to
Hubbard's are made. Our approximate one-electron Green function G is exact in
the atomic limit of zero bandwidth for all S and band filling n, and as n->0
reduces to a dynamical coherent potential approximation (CPA) due to Kubo; we
regard our approximation as a many-body generalisation of Kubo's CPA. G is
calculated self-consistently for general S in the paramagnetic state and for
S=1/2 in a state of arbitrary magnetization. The electronic structure is
investigated and four bands per spin are obtained centred on the atomic limit
peaks of the spectral function. A resistivity formula appropriate to the model
is derived from the Kubo formula and the paramagnetic state resistivity rho is
calculated; insulating states are correctly obtained at n=0 and n=1 for strong
Hund coupling. Our prediction for rho is much too small to be consistent with
experiments on manganites so we agree with Millis et al that the bare DE model
is inadequate. We show that the agreement with experiment obtained by Furukawa
is due to his use of an unphysical density of states.Comment: 20 pages, 8 figures, submitted to J. Phys.: Condens. Matte

### Electron Magnetic Resonance: The Modified Bloch Equation

We find a modified Bloch equation for the electronic magnetic moment when the
magnetic moment explicitly contains a diamagnetic contribution (a magnetic
field induced magnetic moment arising from the electronic orbital angular
momentum) in addition to the intrinsic magnetic moment of the electron. The
modified Bloch is coupled to equations of motion for the position and momentum
operators. In the presence of static and time varying magnetic field
components, the magnetic moment oscillates out of phase with the magnetic field
and power is absorbed by virtue of the magnetic field induced magnetic moment,
even in the absence of coupling to the environment. We explicitly work out the
spectrum and absorption for the case of a $p$ state electron

### Social disruption stress exacerbates alpha-galactosylceramide-induced hepatitis in mice

Objective: Psychosocial stress has been suggested as a possible aggravating factor in liver diseases, however, the underlying mechanism has yet to be clarified. Recently, our research revealed that electric foot-shock stress aggravated NK1.1 Ag+ T cell-dependent a-galactosylceramide (alpha-GalCer)-induced hepatitis in mice via a mechanism mediated by endogenous glucocorticoids. In this study, we examined whether or not such aggravation could be applied to a psychosocially stressful situation, e.g. social disruption stress. Methods: Male wildtype C57BL/6 (B6) or B6 hepatitis virus type B surface antigen transgenic (HBs-tg) mice, a hepatitis B virus carrier mouse model, were exposed 3 times in 1 week to social disruption stress in which an 8-month-old aggressive male intruder was placed into their home cage (5 mice per group) for 2 h. Twelve hours after the final exposure to the stress, the wild-type and HBs-tg mice were intravenously injected with alpha-GalCer. Results:The stress-exposed wild-type mice exhibited significantly reduced thymus weight loss compared with the control animals. Moreover, this stress regimen led to a significant increase in serum alanine aminotransferase levels in both the wild-type and the HBs-tg mice, although the increase in the HBs-tg mice was higher than that in the wild-type mice. Conclusion: These findings demonstrated that, similar to electric foot-shock stress, social disruption stress exacerbated alpha-GalCer-induced hepatitis. Copyright (C) 2005 S. Karger AG, Basel

### D6 Family Symmetry and Cold Dark Matter at LHC

We consider a non-supersymmetric extension of the standard model with a
family symmetry based on D6 Z2 Z2, where one of Z2's is exactly conserved. This
Z2 forbids the tree-level neutrino masses and simultaneously ensures the
stability of cold dark matter candidates. From the assumption that cold dark
matter is fermionic we can single out the D6 singlet right-handed neutrino as
the best cold dark mater candidate. We find that an inert charged Higgs with a
mass between 300 and 750 GeV decays mostly into an electron (or a positron)
with a large missing energy, where the missing energy is carried away by the
cold dark matter candidate. This will be a clean signal at LHC.Comment: 20 pages, 7 figure

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