415 research outputs found
The Sphaleron Barrier in the Presence of Fermions
We calculate the minimal energy path over the sphaleron barrier in the
pre\-sen\-ce of fermions, assuming that the fermions of a doublet are
degenerate in mass. This allows for spherically symmetric ans\"atze for the
fields, when the mixing angle dependence is neglected. While light fermions
have little influence on the barrier, the presence of heavy fermions ( TeV) strongly deforms the barrier, giving rise to additional sphalerons
for very heavy fermions ( 10 TeV). Heavy fermions form
non-topological solitons in the vacuum sector.Comment: 19 pages, latex, 18 figures in 3 seperate uuencoded postscript files
THU-93/1
Nondegenerate Fermions in the Background of the Sphaleron Barrier
We consider level crossing in the background of the sphaleron barrier for
nondegenerate fermions. The mass splitting within the fermion doublets allows
only for an axially symmetric ansatz for the fermion fields. In the background
of the sphaleron we solve the partial differential equations for the fermion
functions. We find little angular dependence for our choice of ansatz. We
therefore propose a good approximate ansatz with radial functions only. We
generalize this approximate ansatz with radial functions only to fermions in
the background of the sphaleron barrier and argue, that it is a good
approximation there, too.Comment: LATEX, 20 pages, 11 figure
Probing Exotic Physics With Cosmic Neutrinos
Traditionally, collider experiments have been the primary tool used in
searching for particle physics beyond the Standard Model. In this talk, I will
discuss alternative approaches for exploring exotic physics scenarios using
high energy and ultra-high energy cosmic neutrinos. Such neutrinos can be used
to study interactions at energies higher, and over baselines longer, than those
accessible to colliders. In this way, neutrino astronomy can provide a window
into fundamental physics which is highly complementary to collider techniques.
I will discuss the role of neutrino astronomy in fundamental physics,
considering the use of such techniques in studying several specific scenarios
including low scale gravity models, Standard Model electroweak instanton
induced interactions, decaying neutrinos and quantum decoherence.Comment: 11 pages, 6 figures; For the proceedings of From Colliders To Cosmic
Rays, Prague, Czech Republic, September 7-13, 200
Level Crossing Along Sphaleron Barriers
In the electroweak sector of the standard model topologically inequivalent
vacua are separated by finite energy barriers, whose height is given by the
sphale\-ron. For large values of the Higgs mass there exist several sphaleron
solutions and the barriers are no longer symmetric. We construct paths of
classical configurations from one vacuum to a neighbouring one and solve the
fermion equations in the background field configurations along such paths,
choosing the fermions of a doublet degenerate in mass. As in the case of light
Higgs masses we observe the level crossing phenomenon also for large Higgs
masses.Comment: 17 pages, latex, 10 figures in uuencoded postscript files. THU-94/0
Recovery of the old nova V840 Ophiuchi: A carbon rich system
We present optical spectroscopy and multi colour photometry of the old nova
V840 Oph. We rediscovered the nova based on its position in the colour--colour
diagrams. It stands out as a very blue object with an additional red component.
We present the first optical spectroscopy of this candidate and confirm its
nova character. Furthermore, V840\,Oph has been found as one of very few
cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the
analysis of the carbon lines it seems probable that V840 Oph contains actually
a carbon-rich secondary star. So far, only the nova-like QU Car has been known
to have such a companion. We furthermore find spectroscopic evidence that V840
Oph has a hot, dense accretion disc or stream and is probably a magnetic
system.Comment: 7 pages, 6 figures, accepted by A&
The beta functions of a scalar theory coupled to gravity
We study a scalar field theory coupled to gravity on a flat background, below
Planck's energy. Einstein's theory is treated as an effective field theory.
Within the context of Wilson's renormalization group, we compute gravitational
corrections to the beta functions and the anomalous dimension of the scalar
field, taking into account threshold effects.Comment: 13 pages, plainTe
Infrared Properties of Cataclysmic Variables from 2MASS: Results from the 2nd Incremental Data Release
Because accretion-generated luminosity dominates the radiated energy of most
cataclysmic variables, they have been ``traditionally'' observed primarily at
short wavelengths. Infrared observations of cataclysmic variables contribute to
the understanding of key system components that are expected to radiate at
these wavelengths, such as the cool outer disk, accretion stream, and secondary
star. We have compiled the J, H, and Ks photometry of all cataclysmic variables
located in the sky coverage of the 2 Micron All Sky Survey (2MASS) 2nd
Incremental Data Release. This data comprises 251 systems with reliably
identified near-IR counterparts and S/N > 10 photometry in one or more of the
three near-IR bands.Comment: 2 pages, including 1 figure. To appear in the proceedings of The
Physics of Cataclysmic Variables and Related Objects, Goettingen, Germany.
For our followup ApJ paper (in press), also see
http://www.ctio.noao.edu/~hoard/research/2mass/index.htm
Wavepacket Dynamics in Yang-Mills Theory
We discuss the results of numerical simulations of colliding wavepackets in
Yang--Mills theory. We investigate their behavior as a function of
amplitude and momentum distribution. We find regions in our parameter space in
which initial wave packets scatter into final configurations with dramatically
different momentum distributions. These results constitute new classical
trajectories with multiparticle boundary conditions. We explain their relevance
for the calculation of scattering amplitudes in the semiclassical
approximation. Finally, we give directions for future work.Comment: 11 pgs. text, 11 optional figs using PiCTeX and epsf, new version
contains improved discussion of scaling properties of results and one
additional figure
Real-Time Instantons and Suppression of Collision-Induced Tunneling
We consider tunneling processes in QFT induced by collisions of elementary
particles. We propose a semiclassical method for estimating the probability of
these processes in the limit of very high collision energy. As an illustration,
we evaluate the maximum probability of induced tunneling between different
vacua in a (1+1)-dimensional scalar model with boundary interaction.Comment: 5 pages, 1 figure, JETP Letters styl
Chaotic Symmetry Breaking and Dissipative Two-Field Dynamics
The dynamical symmetry breaking in a two-field model is studied by
numerically solving the coupled effective field equations. These are
dissipative equations of motion that can exhibit strong chaotic dynamics. By
choosing very general model parameters leading to symmetry breaking along one
of the field directions, the symmetry broken vacua make the role of transitory
strange attractors and the field trajectories in phase space are strongly
chaotic. Chaos is quantified by means of the determination of the fractal
dimension, which gives an invariant measure for chaotic behavior. Discussions
concerning chaos and dissipation in the model and possible applications to
related problems are given.Comment: 18 pages, 2 .eps figures (uses epsf), Revtex. A much larger version,
more comments, refs. and results. Version in press Physical Review
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