1,044 research outputs found
Decoherence due to thermal effects in two quintessential quantum systems
Decoherence effects at finite temperature (T) are examined for two manifestly
quantum systems: (i) Casimir forces between parallel plates that conduct along
different directions, and (ii) a topological Aharonov-Bohm (AB) type force
between fluxons in a superconductor. As we illustrate, standard path integral
calculations suggest that thermal effects may remove the angular dependence of
the Casimir force in case (i) with a decoherence time set by h/(k_{B} T) where
h is Plank's constant and k_{B} is the Boltzmann constant. This prediction may
be tested. The effect in case (ii) is due a phase shift picked by unpaired
electrons upon encircling an odd number of fluxons. In principle, this effect
may lead to small modifications in Abrikosov lattices. While the AB forces
exist at extremely low temperatures, we find that thermal decoherence may
strongly suppress the topological force at experimentally pertinent finite
temperatures. It is suggested that both cases (i) and (ii) (as well as other
examples briefly sketched) are related to a quantum version of the
fluctuation-dissipation theorem.Comment: 15 pages, 2 figure
Now You See It, Now You Don't--The Pattern of Production of Certain Resonances
We try to motivate from QCD a pattern of production in various reactions of
(non)exotic resonances. A higher penalty for extra q\bar{q} production in e^+
e^- collisions than in collisions with a nucleon target may explain the absence
of exotic multi-quark states in e^+ e^- . We also briefly address the
doubly-charmed baryons and the utilization of QCD inequalities in connection
with possible new hadronic states.Comment: 11 page
Signs and Polarized/Magnetic versions of the Casimir Forces
We consider versions of the Casimir effect where the force can be controlled
by changing the angle between two Casimir ``plates'' or the temperature of two
nearby rings. We also present simple arguments for the sign of Casimir forces.Comment: 3 pages of double column revtex, + 4 figures. For correspondence use
Tel Aviv address, or [email protected]
Some Comments on the Putative (1543) Exotic State
We point out that existing scattering data available in the PDG
(Particle Data Group compilation) suggest some fluctuations in those momentum
bins where the (Fermi motion broadened) [1543] resonance recently
indicated in many gamma nuclear reactions and predicted six years ago by
Diakonv Petrov and Polyakov might have shown up. The I=0, P-wave
channel should have a universal peak cross section of mb at
resonance. The smallness of the effect seen in with the
fluctuations being less than 4 mb imply an indirect bound MeV, far stronger than the direct gamma-d measurements. This renders the
theoretical interpretation of the new state very difficult.Comment: 10 pages, no figures, RevTex
QCD Inequalities and the
We discuss the new state discovered by BaBar and demonstrate
using QCD inequalities that if indeed the and the new
() are primarilly made of four quarks that a new I=0 `` bound
state'' at a mass smaller than 3660 MeV must exist. Observation of such a state
will constitute definitive evidence for four-quark states
Correlated Scattering and Cluster Planes
We suggest a new correlation in diffractive production of 2 ``clusters''
with large intrinsic angular momenta for each
and cluster. These correlations are expected in the context of the
``color dipole picture'' for high energy collision and reflect the approximate
conservation of dipole direction during the collision. This conservation is in
particular manifest when the two dipoles, , and the impact
vector \undtilb are all parallel. The predicted positive triple correlation
is between the momentum transfer \undtildel and the planes of the
and clusters.Comment: 8 pages, late
Testing Violations of Lorentz Invariance with Cosmic Rays
Cosmic rays are the highest energy particles available for our study and as
such serve as excellent probes of the effects of Lorentz Invariance Violations,
which are expected to increase with energy. This general paradigm is
investigated in this paper by studying the effects of such violations within
the Coleman-Glashow model in which each particle species may have its own
maximum attainable velocity, even exceeding that of light \textit{in vacuo}.
The particular focus here is that the muon neutrino may have the maximum speed
exceeding that of light. We show that such an assumption leads to the
elongation of the decay lifetime of the pion that increases with energy over
and above the time dilation effects. We provide a transparent analytical
derivation of the spectral intensities of muon neutrinos and muons generated in
the Earth's atmosphere by cosmic rays. In this derivation we not only account
for elongation of the pion lifetime, but also for the loss of energy by the
neutrinos by radiation of the electron-positron pairs through the Cohen-Glashow
process, during their propagation. We then compare the theoretical spectra with
observations of neutrinos and muons from large instruments like IceCube and
BUST to set a limit of on the fractional excess speed of
neutrinos over that of light. We also show that the ratio of the spectral
intensities of downward and upward moving neutrinos at various angles
constitute a diagnostic exclusively for the Cohen-Glashow process, which may be
searched for in the IceCube data set. We conclude the paper with several
comments, including those related to improvements of these tests when definite
signals of GZK neutrinos will be observed.Comment: version 2, 28 pages, 10 figure
Some Speculations on the Ultimate Planck Energy
The inability to achieve in the present universe, via electromagnetic or
gravitational acceleration, Planck energies for elementary particles is
suggested on the basis of several, some relatively sophisticated, failed
attempts. This failure is essential for schemes were the superplanckian regime
for the energies of elementary particles is ``Unphysical''. The basic
observation is that this failure to achieve superplanckian energies naturally
occurs in our universe of finite age and horizon. It does tie up in a
mysterious fashion these cosmological quantities and elementary physics
parameters such as the masses of the lightest charged fermions.Comment: 11 pages, latex, 4 figures. For ALL CORRESPONDENCE contact
[email protected]
Are there non-strange low-lying penta-quarks and can we understand their width
We argue that the lightest isospin 1/2 partners of the Z^+(1530) s(bar)uudd
penta-quark predicted by Diakonov, Petrov and Polyakov are not the N(1710)
mixed anti-decuplet states, but the pure non-strange u(bar)(ud)(ud) and
d(bar)(ud)(ud) penta-quark states which may lie as low as 1200 MeV. The
expected low width of a few MeV of such a putative state may explain why it was
missed in phase shift analyzes of pion-nucleon scattering.Comment: 11 pages, 1 figur
Bimaximal Neutrino Mixing and Neutrino Mass Matrix
We show that the bimaximal neutrino mixing pattern suggested by the solar and
atmospheric neutrino data can be derived from the maximal, symmetric, four
neutrino mixing in the limit that one of the neutrinos is made heavy. Imposing
the constraints of no neutrinoless double beta decay and a 20% hot dark matter
component of the universe leads to a three neutrino mass matrix recently
suggested by Georgi and Glashow. Our result can be useful in constructing
theoretical models for the bimaximal pattern. We illustrate this by a simple
example.Comment: New material strengthening the argument of the paper added; 10 pages
latex; UMD-PP-99-2
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