7,002 research outputs found
LHC Symposium 2003: Summary Talk
This summary talk reviews the LHC 2003 Symposium, focusing on expectations as
we prepare to leap over the current energy frontier into new territory. We may
learn from what happened in the two most recent examples of leaping into new
energy territory. Quite different scenarios appeared in those two cases. In
addition, we review the status of the machine and experiments as reported at
the Symposium. Finally, I suggest an attitude which may be most appropriate as
we look forward to the opportunities anticipated for the first data from the
LHC.Comment: Summary Talk: LHC Symposium, May 1-3, 2003, Fermilab, Batavia, IL US
Review of Heavy-Quark Production at Fixed-Target Experiments
An increasingly large amount of quality fixed-target data on heavy-quark production at fixed-target energies is appearing. This data can provide information across a range of physics topics. The topics vary from investigations of QCD predictions to the understanding of the structure of hadrons. Recent results on neutrino, photon, and hadron production of charm and beauty will be reviewed in this context. The greatest insight will come from combining multiple measurements as they relate to the physics topics, and by ensuring that the parameters used in models are consistent with all the measurements. We have not yet really entered the time when this has been done for fixed-target measurements
Photoemission spectroscopy and sum rules in dilute electron-phonon systems
A family of exact sum rules for the one-polaron spectral function in the
low-density limit is derived. An algorithm to calculate energy moments of
arbitrary order of the spectral function is presented. Explicit expressions are
given for the first two moments of a model with general electron-phonon
interaction, and for the first four moments of the Holstein polaron. The sum
rules are linked to experiments on momentum-resolved photoemission
spectroscopy. The bare electronic dispersion and the electron-phonon coupling
constant can be extracted from the first and second moments of spectrum. The
sum rules could serve as constraints in analytical and numerical studies of
electron-phonon models.Comment: 4 page
Reformulation of the Stochastic Potential Switching Algorithm and a Generalized Fourtuin-Kasteleyn Representation
A new formulation of the stochastic potential switching algorithm is
presented. This reformulation naturally leads us to a generalized
Fourtuin-Kasteleyn representation of the partition function Z. A formula for
internal energy E and that of heat capacity C are derived from derivatives of
the partition function. We also derive a formula for the exchange probability
in the replica exchange Monte Carlo method. By combining the formulae with the
Stochastic Cutoff method, we can greatly reduce the computational time to
perform internal energy and heat capacity measurements and the replica exchange
Monte Carlo method in long-range interacting systems. Numerical simulations in
three dimensional magnetic dipolar systems show the validity and efficiency of
the method.Comment: 11 pages, 6 figures, to appear in PR
Developments in Rare Kaon Decay Physics
We review the current status of the field of rare kaon decays. The study of
rare kaon decays has played a key role in the development of the standard
model, and the field continues to have significant impact. The two areas of
greatest import are the search for physics beyond the standard model and the
determination of fundamental standard-model parameters. Due to the exquisite
sensitivity of rare kaon decay experiments, searches for new physics can probe
very high mass scales. Studies of the k->pnn modes in particular, where the
first event has recently been seen, will permit tests of the standard-model
picture of quark mixing and CP violation.Comment: One major revision to the text is the branching ratio of KL->ppg,
based on a new result from KTeV. Several references were updated, with minor
modifications to the text. A total of 48 pages, with 28 figures, in LaTeX; to
be published in the Annual Review of Nuclear and Particle Science, Vol. 50,
December 200
Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial Films in Fields up to 50 T''
Recently Wagner et al. [Phys. Rev. Lett. Vol. 81, P. 3980 (1998)] proposed
that Mott's original model be modified to incorporate a hopping barrier which
depends on the misorientation between the spins of electrons at the initial and
the final states in an elementary process. They further claimed that using the
model they can explain the observed scaling behavior--
negative-magnetoresistivity scaling proportional to the Brillouin function
in the ferromagnetic state and to in the paramagnetic
state. In this comment we argue that the modification needed for Mott's
original model is different from that proposed by Wagner et al. and further
show that our picture will successfully explain the observed scaling in the two
regimes.Comment: 1 pag
Quantum coherence and carriers mobility in organic semiconductors
We present a model of charge transport in organic molecular semiconductors
based on the effects of lattice fluctuations on the quantum coherence of the
electronic state of the charge carrier. Thermal intermolecular phonons and
librations tend to localize pure coherent states and to assist the motion of
less coherent ones. Decoherence is thus the primary mechanism by which
conduction occurs. It is driven by the coupling of the carrier to the molecular
lattice through polarization and transfer integral fluctuations as described by
the hamiltonian of Gosar and Choi. Localization effects in the quantum coherent
regime are modeled via the Anderson hamiltonian with correlated diagonal and
non-diagonal disorder leading to the determination of the carrier localization
length. This length defines the coherent extension of the ground state and
determines, in turn, the diffusion range in the incoherent regime and thus the
mobility. The transfer integral disorder of Troisi and Orlandi can also be
incorporated. This model, based on the idea of decoherence, allowed us to
predict the value and temperature dependence of the carrier mobility in
prototypical organic semiconductors that are in qualitative accord with
experiments
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