43,432 research outputs found
Successful Supersymmetric Inflation
We reconsider the problems of cosmological inflation in effective
supergravity theories. A singlet field in a hidden sector is demonstrated to
yield an acceptable inflationary potential, without fine tuning. In the
simplest such model, the requirement of generating the microwave background
anisotropy measured by COBE fixes the inflationary scale to be about
GeV, implying a reheat temperature of order GeV. This is low enough to
solve the gravitino problem but high enough to allow baryogenesis after
inflation. Such consistency requires that the generation of gravitational waves
be negligible and that the spectrum of scalar density perturbations depart
significantly from scale-invariance, thus improving the fit to large-scale
structure in an universe dominated by cold dark matter. We also consider the
problems associated with gravitino production through inflaton decay and with
other weakly coupled fields such as the moduli encountered in (compactified)
string theories.Comment: 27 pages (LaTeX) including 1 embedded (PostScript) figure. Revised to
include a fuller discussion of initial conditions (leading to "eternal"
inflation) and the role of moduli; some reordering of sections for greater
clarity. Accepted for publication in Nuclear Physics
Lepton non-universality in decays and fermion mass structure
We consider the possibility that the neutral-current anomalies are due to
radiative corrections generated by Yukawa interactions of quarks and leptons
with new vector-like quark and lepton electroweak doublets and new Standard
Model singlet scalars. We show that the restricted interactions needed can
result from an underlying Abelian family symmetry and that the same symmetry
can give rise to an acceptable pattern of quark and charged lepton masses and
mixings, providing a bridge between the non-universality observed in the
B-sector and that of the fermion mass matrices. We construct two simple models,
one with a single singlet scalar in which the flavour changing comes from quark
and lepton mixing and one with an additional scalar in which the flavour
changing can come from both fermion and scalar mixing. We show that for the
case the new quarks are much heavier than the new leptons and scalars the
anomalies can be due to box diagrams with couplings in the perturbative regime
consistent with the bounds coming from , and mixing as well as other lepton family number violating processes. The
new states can be dark matter candidates and, in the two scalar model with a
light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a
simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment
and the dark matter abundance.Comment: Replacement contains few additional reference
Fast, high fidelity information transmission through spin chain quantum wires
Spin chains have been proposed as quantum wires for information transfer in
solid state quantum architectures. We show that huge gains in both transfer
speed and fidelity are possible using a minimalist control approach that relies
only a single, local, on-off switch actuator. Effective switching time
sequences can be determined using optimization techniques for both ideal and
disordered chains. Simulations suggest that effective optimization is possible
even in the absence of accurate models.Comment: revtex4, 4 pages, 5 figure
Research of low cost wind generator rotors
A feasibility program determined that it would be possible to significantly reduce the cost of manufacturing wind generator rotors by making them of cast urethane. Several high modulus urethanes which were structurally tested were developed. A section of rotor was also cast and tested showing the excellent aerodynamic surface which results. A design analysis indicated that a cost reduction of almost ten to one can be achieved with a small weight increase to achieve the same structural integrity as expected of current rotor systems
Investigations on transparent liquid-miscibility gap systems
Sedimentation and phase separation is a well known occurrence in monotectic or miscibility gap alloys. Previous investigations indicate that it may be possible to prepare such alloys in a low-gravity space environment but recent experiments indicate that there may be nongravity dependent phase separation processes which can hinder the formation of such alloys. Such phase separation processes are studied using transparent liquid systems and holography. By reconstructing holograms into a commercial-particle-analysis system, real time computer analysis can be performed on emulsions with diameters in the range of 5 micrometers or greater. Thus dynamic effects associated with particle migration and coalescence can be studied. Characterization studies on two selected immiscible systems including an accurate determination of phase diagrams, surface and interfacial tension measurements, surface excess and wetting behavior near critical solution temperatures completed
Reconstruction of Quark Mass Matrices with Weak Basis Texture Zeroes from Experimental Input
All quark mass matrices with texture zeroes obtained through weak basis
transformations are confronted with the experimental data. The reconstruction
of the quark mass matrices M_u and M_d at the electroweak scale is performed in
a weak basis where the matrices are Hermitian and have a maximum of three
vanishing elements. The same procedure is also accomplished for the Yukawa
coupling matrices at the grand unification scale in the context of the Standard
Model and its minimal supersymmetric extension as well as of the two Higgs
doublet model. The analysis of all viable power structures on the quark Yukawa
coupling matrices that could naturally appear from a Froggatt-Nielsen mechanism
is also presented.Comment: RevTeX4, 3 tables, 21 pages; misprints corrected and one reference
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Turbulent Supernova Shock Waves and the Sterile Neutrino Signature in Megaton Water Detectors
The signatures of sterile neutrinos in the supernova neutrino signal in
megaton water Cerenkov detectors are studied. Time dependent modulation of the
neutrino signal emerging from the sharp changes in the oscillation probability
due to shock waves is shown to be a smoking gun for the existence of sterile
neutrinos. These modulations and indeed the entire neutrino oscillation signal
is found to be different for the case with just three active neutrinos and the
cases where there are additional sterile species mixed with the active
neutrinos. The effect of turbulence is taken into account and it is found that
the effect of the shock waves, while modifed, remain significant and
measurable. Supernova neutrino signals in water detectors can therefore give
unambiguous proof for the existence of sterile neutrinos, the sensitivity
extending beyond that for terrestial neutrino experiments. In addition the time
dependent modulations in the signal due to shock waves can be used to trace the
evolution of the shock wave inside the supernova.Comment: 28 pages, 11 figure
Sequential Flavour Symmetry Breaking
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which
allows for independent unitary transformations of the fermion multiplets. In
the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs
boson, and the resulting fermion masses and mixing angles show a pronounced
hierarchy. In this work we connect the observed hierarchy to a sequence of
intermediate effective theories, where the flavour symmetries are broken in a
step-wise fashion by vacuum expectation values of suitably constructed spurion
fields. We identify the possible scenarios in the quark sector and discuss some
implications of this approach.Comment: 22 pages latex, no figure
Thermal gravity, black holes and cosmological entropy
Taking seriously the interpretation of black hole entropy as the logarithm of
the number of microstates, we argue that thermal gravitons may undergo a phase
transition to a kind of black hole condensate. The phase transition proceeds
via nucleation of black holes at a rate governed by a saddlepoint configuration
whose free energy is of order the inverse temperature in Planck units. Whether
the universe remains in a low entropy state as opposed to the high entropy
black hole condensate depends sensitively on its thermal history. Our results
may clarify an old observation of Penrose regarding the very low entropy state
of the universe.Comment: 5 pages, 2 figures, RevTex. v4: to appear in Phys. Rev.
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