12,815 research outputs found
An evaluation of the NASA Tech House, including live-in test results, volume 1
The NASA Tech House was designed and constructed at the NASA Langley Research Center, Hampton, Virginia, to demonstrate and evaluate new technology potentially applicable for conservation of energy and resources and for improvements in safety and security in a single-family residence. All technology items, including solar-energy systems and a waste-water-reuse system, were evaluated under actual living conditions for a 1 year period with a family of four living in the house in their normal lifestyle. Results are presented which show overall savings in energy and resources compared with requirements for a defined similar conventional house under the same conditions. General operational experience and performance data are also included for all the various items and systems of technology incorporated into the house design
Perturbative Expansion around the Gaussian Effective Action: The Background Field Method
We develop a systematic method of the perturbative expansion around the
Gaussian effective action based on the background field method. We show, by
applying the method to the quantum mechanical anharmonic oscillator problem,
that even the first non-trivial correction terms greatly improve the Gaussian
approximation.Comment: 16 pages, 3 eps figures, uses RevTeX and epsf. Errors in Table 1 are
corrected and new references are adde
Preheating, Supersymmetry Breaking and Baryogenesis
Fluctuations of scalar fields produced at the stage of preheating after
inflation are so large that they can break supersymmetry much stronger than
inflation itself. These fluctuations may lead to symmetry restoration along
flat directions of the effective potential even in the theories where the usual
high temperature corrections are exponentially suppressed. Our results show
that nonthermal phase transitions after preheating may play a crucial role in
the generation of the primordial baryon asymmetry by the Affleck-Dine
mechanism. In particular, the baryon asymmetry may be generated at the very
early stage of the evolution of the Universe, at the preheating era, and not
when the Hubble parameter becomes of order the gravitino mass.Comment: 4 pages, no figure
Infrared Behaviour of Systems With Goldstone Bosons
We develop various complementary concepts and techniques for handling quantum
fluctuations of Goldstone bosons.We emphasise that one of the consequences of
the masslessness of Goldstone bosons is that the longitudinal fluctuations also
have a diverging susceptibility characterised by an anomalous dimension
in space-time dimensions .In these fluctuations diverge
logarithmically in the infrared region.We show the generality of this
phenomenon by providing three arguments based on i). Renormalization group
flows, ii). Ward identities, and iii). Schwinger-Dyson equations.We obtain an
explicit form for the generating functional of one-particle irreducible
vertices of the O(N) (non)--linear --models in the leading 1/N
approximation.We show that this incorporates all infrared behaviour correctly
both in linear and non-linear -- models. Our techniques provide an
alternative to chiral perturbation theory.Some consequences are discussed
briefly.Comment: 28 pages,2 Figs, a new section on some universal features of
multipion processes has been adde
Dissipation in equations of motion of scalar fields
The methods of non-equilibrium quantum field theory are used to investigate
the possibility of representing dissipation in the equation of motion for the
expectation value of a scalar field by a friction term, such as is commonly
included in phenomenological inflaton equations of motion. A sequence of
approximations is exhibited which reduces the non-equilibrium theory to a set
of local evolution equations. However, the adiabatic solution to these
evolution equations which is needed to obtain a local equation of motion for
the expectation value is not well defined; nor, therefore, is the friction
coefficient. Thus, a non-equilibrium treatment is essential, even for a system
that remains close to thermal equilibrium, and the formalism developed here
provides one means of achieving this numerically.Comment: 17 pages, 5 figure
Calculation of Particle Production by Nambu Goldstone Bosons with Application to Inflation Reheating and Baryogenesis
A semiclassical calculation of particle production by a scalar field in a
potential is performed. We focus on the particular case of production of
fermions by a Nambu-Goldstone boson . We have derived a (non)local
equation of motion for the -field with the backreaction of the produced
particles taken into account. The equation is solved in some special cases,
namely for purely Nambu-Goldstone bosons and for the tilted potential . Enhanced production of bosons due to
parametric resonance is investigated; we argue that the resonance probably
disappears when the expansion of the universe is included. Application of our
work on particle production to reheating and an idea for baryogenesis in
inflation are mentioned.Comment: Submitted to Physical Review {\rm D}: October 4, 1994 21 page, UM-AC
94-3
Enhanced baryon number violation due to cosmological defects with localized fermions along extra dimension
We propose a new scenario of baryon number violation in models with extra
dimensions. In the true vacuum, baryon number is almost conserved due to the
localization mechanism of matter fields, which suppresses the interactions
between quarks and leptons. We consider several types of cosmological defects
in four-dimensional spacetime that shift the center of the localized matter
fields, and show that the magnitudes of the baryon number violating
interactions are well enhanced. Application to baryogenesis is also discussed.Comment: 12pages, latex2e, added references, to appear in PR
Non-transversality of the gluon polarization tensor in a chromomagnetic background
We investigate the question about the transversality of the gluon
polarization tensor in a homogeneous chromomagnetic background field. We
re-derive the non transversality known from a pure one loop calculation using
the Slavnov-Taylor identities. In addition we generalize the procedure to
arbitrary gauge fixing parameter and calculate the -dependent part
of the polarization tensor.Comment: subm. to TM
Systematic Study of the Kaon to Pion Multiplicity Ratios in Heavy-Ion Collisions
We present a systematic study of the kaon to pion multiplicity ratios (K+/pi+
and K-/pi-) in heavy-ion collisions from AGS to RHIC energy using the
Relativistic Quantum Molecular Dynamics (RQMD) model. The model satisfactorily
describes the available experimental data on K+/pi+ and K-/pi-. Within the
model, we find that the strong increase of the ratios with the number of
participants is mainly due to hadronic rescattering of produced mesons with
ingoing baryons and their resonances. The enhancement of K/pi in heavy-ion
collisions with respect to elementary p+p interactions is larger at AGS energy
than SPS energy, and decreases smoothly with bombarding energy. The total
multiplicity ratios at RHIC energy are predicted by RQMD to be K+/pi+ = 0.19
and K-/pi- = 0.15.Comment: 10 pages, 8 figures, RevTeX style. A section is added to discuss
effects of rope formatio
Searching for prompt signatures of nearby core-collapse supernovae by a joint analysis of neutrino and gravitational-wave data
We discuss the science motivations and prospects for a joint analysis of
gravitational-wave (GW) and low-energy neutrino data to search for prompt
signals from nearby supernovae (SNe). Both gravitational-wave and low-energy
neutrinos are expected to be produced in the innermost region of a
core-collapse supernova, and a search for coincident signals would probe the
processes which power a supernova explosion. It is estimated that the current
generation of neutrino and gravitational-wave detectors would be sensitive to
Galactic core-collapse supernovae, and would also be able to detect
electromagnetically dark SNe. A joint GW-neutrino search would enable
improvements to searches by way of lower detection thresholds, larger distance
range, better live-time coverage by a network of GW and neutrino detectors, and
increased significance of candidate detections. A close collaboration between
the GW and neutrino communities for such a search will thus go far toward
realizing a much sought-after astrophysics goal of detecting the next nearby
supernova.Comment: 10 pages, 3 figures. To appear in Class. Quantum Gra
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