55,794 research outputs found
Classical issues in electroweak baryogenesis
In one scenario of baryogenesis, the matter-antimatter asymmetry was
generated in the early universe during a cold electroweak transition. We model
this transition by changing the sign of the effective mass-squared parameter of
the Higgs field from positive to negative. The resulting `tachyonic'
instability leads to a rapid growth of occupation numbers, such that a
classical approximation can be made in computing subsequent developments in
real time.
We solve the classical equations of motion in the SU(2)-Higgs model under the
influence of effective CP-violation. The resulting baryon asymmetry follows
from the generated Chern-Simons number using the anomaly equation. The
`classical' difficulties with lattice implementations of these observables are
avoided here because the fields are smooth on the lattice scale.Comment: Proceedings Lattice 2003 (Higgs), 3 pages; added reference
Branched chain aldehydes: production and breakdown pathways and relevance for flavour in foods
Branched aldehydes, such as 2-methyl propanal and 2- and 3-methyl butanal, are important flavour compounds in many food products, both fermented and non-fermented (heat-treated) products. The production and degradation of these aldehydes from amino acids is described and reviewed extensively in literature. This paper reviews aspects influencing the formation of these aldehydes at the level of metabolic conversions, microbial and food composition. Special emphasis was on 3-methyl butanal and its presence in various food products. Knowledge gained about the generation pathways of these flavour compounds is essential for being able to control the formation of desired levels of these aldehydes
Manifestly Gauge Invariant Models of Chiral Lattice Fermions
A manifestly gauge invariant lattice action for nonanomalous chiral models is
proposed which leads in the continuum limit to the theory free of doublers.Comment: 9 pages, LaTeX. Revised version with an extended discussion of the
role of higher derivative regulators. Submitted to Phys.Lett.B. Preprint
SMI-9-9
Staggered fermions for chiral gauge theories: Test on a two-dimensional axial-vector model
As a first step towards constructing chiral models on the lattice with
staggered fermions, we study a U(1) model with axial-vector coupling to an
external gauge field in two dimensions. In our approach gauge invariance is
broken, but it is restored in the classical continuum limit. We find that the
continuum divergence relations for the vector and axial-vector currents are
reproduced, up to contact terms, which we determine analytically. The current
divergence relations are also studied numerically for smooth external gauge
fields with topological charge zero. We furthermore investigate the effect of
fluctuating gauge transformations and of gauge configurations with non-trivial
topological charge.Comment: 17 pages, 5 postscript figures (appended), ITFA 93-13, UCSD/PTH 93-1
Reverse flow catalytic membrane reactors for energy efficient syngas production
To improve the recuperative heat exchange, a Reverse Flow Catalytic Membrane Reactor (RFCMR) with porous membranes is proposed in this thesis, in which very efficient heat exchange between the feed and product streams is achieved by using the reverse flow concept (i.e. periodic alternation of the flow direction of the gas through a fixed catalyst bed)
No strong coupling regime in the fermion-Higgs sector of the standard model
We present results for the renormalized quartic self-coupling \lm_R and the
renormalized Yukawa coupling in a fermion-Higgs model with two SU(2)
doublets, indicating that these couplings are not very strong.Comment: 4 pages, 4 postscript figures (appended), ITFA-92-32, HLRZ-92-92,
UCSD/PTH 92-43, Contribution to the Conference Lattice'9
Cold Electroweak Baryogenesis
We present arguments that the CKM CP-violation in the standard model may be
sufficient for the generation of the baryon asymmetry, if the electroweak
transition in the early universe was of the cold, tachyonic, type after
electroweak-scale inflation. A model implementing this is described which
complies with the CMB constraints and which is falsifiable with the LHC.
Numerical simulations of the tachyonic transition with an effective CP-bias
indicate that the observed baryon asymmetry can be generated this way.Comment: 10 pages, 4 figures, presented at Strong and ElectroWeak Matter 200
Real time simulations and the electroweak phase transition
We review recent developments in real-time simulations of SU(2)-Higgs theory
near the electroweak transition and related topics.Comment: 6 pages, latex, 4 figures; to appear in the proceedings of LATTICE
'9
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