178,022 research outputs found
Gauge Theory of Gravity Requires Massive Torsion Field
One of the greatest unsolved issues of the physics of this century is to find
a quantum field theory of gravity. According to a vast amount of literature
unification of quantum field theory and gravitation requires a gauge theory of
gravity which includes torsion and an associated spin field. Various models
including either massive or massless torsion fields have been suggested. We
present arguments for a massive torsion field, where the probable rest mass of
the corresponding spin three gauge boson is the Planck mass.Comment: 3 pages, Revte
Remote Camera and Trapping Survey of the Deep-water Shrimps Heterocarpus laevigatus and H. ensifer and the Geryonid Crab Chaceon granulatus in Palau
Time-lapse remote photo-sequences at 73-700 m depth off Palau, Western Caroline Islands, show that the caridean shrimp Heterocarpus laevigatus tends to be a solitary animal, occurring below ~350 m, that gradually accumulates around bait sites over a prolonged period. A smaller speies, H. ensifer, tends to move erratically in swarms, appearing in large numbers in the upper part of its range (<250 m) during the evening crepuscular period and disappearing at dawn. Trapping and photsequence data indicate the depth range of H. ensifer (during daylight) is ~250-550 M, while H. laevigatus ranges from 350 m to at least 800 m, along with the geryonid crab Chaceon granulatus. Combined trapping for Heterocarpus laevigatus and Chaceon granulatus, using a three-chamber box-trap and extended soak times (48-72 hr), may be an appropriate technique for small-scale deep-water fisheries along forereef slopes of Indo-Pacific archipelagoes
On Inhomogeneity of a String Bit Model for Quantum Gravity
We study quantum gravitational effect on a two-dimensional open universe with
one particle by means of a string bit model. We find that matter is necessarily
homogeneously distributed if the influence of the particle on the size of the
universe is optimized.Comment: 16 pages, LaTeX2
Wind-tunnel tests of wide-chord teetering rotors with and without outboard flapping hinges
Wind tunnel tests of aeroelastically designed helicopter rotor models were conducted to obtain rotor aerodynamic performance and dynamic response data pertaining to two-bladed teetering rotors with a wider chord and lower hover tip speed than currently employed on production helicopters. The effects of a flapping hinge at 62 percent radius were also studied. Finally, the effects of changing tip mass on operating characteristics of the rotor with the outboard flapping hinge were examined. The models were tested at several shaft angles of attack for five advance ratios, 0.15, 0.25, 0.35, 0.40, and 0.45. For each combination of shaft angle and advance ratio, the rotor lift was varied over a wide range to include simulated maneuver conditions. At each test condition, rotor aerodynamic performance and dynamic response data were obtained. From these tests, it was found that wide-chord rotors may be subject to large control forces. An outboard flapping hinge may be used to reduce beamwise bending moments over a significant part of the blade radius without significantly affecting the chordwise bending moments
Universal pulse sequence to minimize spin dephasing in the central spin decoherence problem
We present a remarkable finding that a recently discovered [G. S. Uhrig,
Phys. Rev. Lett. 98, 100504 (2007)] series of pulse sequences, designed to
optimally restore coherence to a qubit in the spin-boson model of decoherence,
is in fact completely model-independent and generically valid for arbitrary
dephasing Hamiltonians given sufficiently short delay times between pulses. The
series maximizes qubit fidelity versus number of applied pulses for
sufficiently short delay times because the series, with each additional pulse,
cancels successive orders of a time expansion for the fidelity decay. The
"magical" universality of this property, which was not appreciated earlier,
requires that a linearly growing set of "unknowns" (the delay times) must
simultaneously satisfy an exponentially growing set of nonlinear equations that
involve arbitrary dephasing Hamiltonian operators.Comment: Published in PRL, revise
Origin of Superconductivity in Boron-doped Diamond
Superconductivity of boron-doped diamond, reported recently at T_c=4 K, is
investigated exploiting its electronic and vibrational analogies to MgB2. The
deformation potential of the hole states arising from the C-C bond stretch mode
is 60% larger than the corresponding quantity in MgB2 that drives its high Tc,
leading to very large electron-phonon matrix elements. The calculated coupling
strength \lambda ~ 0.5 leads to T_c in the 5-10 K range and makes phonon
coupling the likely mechanism. Higher doping should increase T_c somewhat, but
effects of three dimensionality primarily on the density of states keep doped
diamond from having a T_c closer to that of MgB2.Comment: Four pages with two embedded figures, corrected fig1. (To appear in
Physical Review Letters(2004)
Dirac's Observables for the SU(3)XSU(2)XU(1) Standard Model
The complete, missing, Hamiltonian treatment of the standard SU(3)xSU(2)xU(1)
model with Grassmann-valued fermion fields in the Higgs phase is given. We
bypass the complications of the Hamiltonian theory in the Higgs phase,
resulting from the spontaneous symmetry breaking with the Higgs mechanism, by
studying the Hamiltonian formulation of the Higgs phase for the gauge
equivalent Lagrangian in the unitary gauge. A canonical basis of Dirac's
observables is found and the reduced physical Hamiltonian is evaluated. Its
self-energy part is nonlocal for the electromagnetic and strong interactions,
but local for the weak ones. Therefore, the Fermi 4-fermion interaction
reappears at the nonperturbative level.Comment: 90 pages, RevTeX, no figure
Uses of a small field value which falls from a metastable maximum over cosmological times
We consider a small, metastable maximum vacuum expectation value of
order of a few eV, for a pseudoscalar Goldstone-like field, which is related to
the scalar inflaton field in an idealized model of a cosmological,
spontaneously-broken chiral symmetry. The b field allows for relating
semi-quantitatively three distinct quantities in a cosmological context.
(1) A very small, residual vacuum energy density or effective cosmological
constant of ~ lambda b_0^4 ~ 2.7 x 10^{-47}GeV^4, for lambda ~ 3 x 10^{-14},
the same as an empirical inflaton self-coupling.
(2) A tiny neutrino mass, less then b_0.
(3) A possible small variation downward of the proton to electron mass ratio
over cosmological time. The latter arises from the motion downward of the
field over cosmological time, toward a nonzero limiting value as . Such behavior is consistent with an equation of motion.
We argue that hypothetical b quanta, potentially inducing new long-range
forces, are absent, because of negative, effective squared mass in an equation
of motion for -field fluctuations.Comment: version accepted for publication in Mod.Phys.Lett.
On mixing angles and magnetic moment of heavy tau neutrino
If the magnetic moment of unstable tau neutrinos with the mass of (MeV) is
in the region of , it is compatible with the present experimental and
cosmological bounds.
It is pointed out here, that if the tau neutrino has such a large magnetic
moment and can oscillate into a neutrino of another flavour the results from
scattering experiment at LAMPF constrain the tau neutrino mixing angles
to and
depending on the magnetic
moment value in the allowed region.Comment: 5 pages, LaTe
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