1,518 research outputs found
The Electroweak Phase Transition
The electroweak phase transition is investigated by means of the
perturbatively calculated high temperature effective potential. An analytic
result to order is presented for the Abelian Higgs model, the
SU(2)-Higgs model and the standard model and a complete on-shell
renormalization at zero temperature is performed. Higher order corrections are
found to increase the strength of the first order phase transition in the
non-Abelian model, opposite to the Abelian case. This effect is traced back to
the infrared contributions from the typical non-Abelian diagrams. The
dependence of several phase transition parameters on the Higgs mass is analysed
in detail. A new, gauge invariant, approach based on the composite field
is introduced. This method, which supports the above Landau
gauge results numerically, permits a conceptually simpler treatment of the
thermodynamics of the phase transition. In particular, it enables a
straightforward comparison with lattice data and the application of the
Clausius-Clapeyron equation to the electroweak phase transition.Comment: Ph.D. thesis, 70 pages LaTeX, figures not included, complete ps-file
or hardcopy available from the Autho
On Dynamical Adjustment Mechanisms for the Cosmological Constant
After recalling why dynamical adjustment mechanisms represent a particularly
attractive possibility for solving the cosmological constant problem, we
briefly discuss their intrinsic difficulties as summarized in Weinberg's no-go
theorem. We then comment on some problems of the recently proposed
`self-tuning' mechanism in 4+1 dimensions. Finally, we describe an alternative
approach which uses the time-evolution of the universe to achieve a dynamical
relaxation of the cosmological constant to zero.Comment: 4 pages LaTeX, talk at PASCOS 2001, Chapel Hill, North Carolina,
10-15 April 200
Non-Perturbative High-Energy QCD
It is the aim of this talk to review our understanding of the high-energy
limit of QCD, focussing, in particular, on recent theoretical developments.
After a brief introduction, I will recall why the true high-energy limit of QCD
scattering processes is genuinly non-perturbative and why it has so far not
been possible to apply lattice methods to this type of physics. Given the
experimental fact of slowly rising hadronic cross sections, we are thus faced
with a fundamental problem comparable to that of confinement but without the
promise of the lattice. During the last years, the experimental side of this
field has largely been driven by the HERA accelerator, which has, naturally,
also influenced recent theoretical work in high-energy QCD. I will therefore
devote the second part of the talk to small-x deep inelastic scattering, in
particular the physics of diffraction, and attempt to describe its impact on
the wider field of non-perturbative high-energy QCD.Comment: 20 pages LaTeX, 10 figures, Plenary talk at the International
Europhysics Conference on High Energy Physics (EPS HEP 2001), Budapest, 12-18
July 2001, reference adde
High-Energy Scattering and Diffraction: Theory Summary
New developments in the theory and phenomenology of high-energy scattering
and diffraction that were presented and discussed at DIS2000 are reviewed.Comment: 9 pages, LaTeX, including one PostScript figure. Talk given at the
8th International Workshop on Deep-Inelastic Scattering (DIS2000), 25th-30th
April 2000, Liverpool, England, to appear in the proceeding
Precision Unification and Proton Decay in F-Theory GUTs with High Scale Supersymmetry
F-theory GUTs provide a promising UV completion for models with approximate
gauge coupling unification, such as the (non-supersymmetric) Standard Model.
More specifically, if the superparters have masses well above the TeV scale,
the resulting imperfection in unification can be accounted for by the, in
principle calculable, classical F-theory correction at the high scale. In this
paper we argue for the correct form of the F-theory corrections to unification,
including KK mode loop effects. However, the price of compensating the
imprecise unification in such High Scale SUSY models with F-theory corrections
is that the GUT scale is lowered, potentially leading to a dangerously high
proton decay rate from dimension-6 operators. We analyse the possibility of
suppressing the decay rate by the localization of gauge bosons in higher
dimensions. While this effect can be very strong for the zero modes, we find
that in the simplest models of this type it is difficult to realize a
significant suppression for higher modes (Landau levels). Notably, in the
absence of substantial suppressions to the proton decay rate, the superpartners
must be lighter than 100 TeV to satisfy proton decay constraints. We highlight
that multiple correlated signals of proton decay could verify this scenario.Comment: 44 pages. v2: References adde
Calculating the diffractive from the inclusive structure function
It is demonstrated that the global properties of the rapidity gap events at
HERA can be understood based on electron-gluon scattering and a
non-perturbative mechanism of colour neutralization. Using the measured
inclusive structure function to determine the parameters of the parton
model, the diffractive structure function is predicted. The ratio of
diffractive and inclusive cross sections, , is determined by the probability of the produced quark-antiquark pair to
evolve into a colour singlet state.Comment: talk at Workshop on DIS and QCD, Paris, April 1995, 3 pages LaTeX,
uses qcdparis.sty, 2 figures (uuencoded
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