1,799 research outputs found
On "dynamical mass" generation in Euclidean de Sitter space
We consider the perturbative treatment of the minimally coupled, massless,
self-interacting scalar field in Euclidean de Sitter space. Generalizing work
of Rajaraman, we obtain the dynamical mass m^2 \propto sqrt{lambda} H^2 of the
scalar for non-vanishing Lagrangian masses and the first perturbative quantum
correction in the massless case. We develop the rules of a systematic
perturbative expansion, which treats the zero-mode non-perturbatively, and goes
in powers of sqrt{lambda}. The infrared divergences are self-regulated by the
zero-mode dynamics. Thus, in Euclidean de Sitter space the interacting,
massless scalar field is just as well-defined as the massive field. We then
show that the dynamical mass can be recovered from the diagrammatic expansion
of the self-energy and a consistent solution of the Schwinger-Dyson equation,
but requires the summation of a divergent series of loop diagrams of
arbitrarily high order. Finally, we note that the value of the long-wavelength
mode two-point function in Euclidean de Sitter space agrees at leading order
with the stochastic treatment in Lorentzian de Sitter space, in any number of
dimensions.Comment: LaTeX, 15 page
with a warped bulk Higgs
We study the decay in Randall-Sundrum models with an
IR-localised bulk Higgs. The two models under consideration are a minimal model
as well as a model with a custodial protection mechanism. We include the
effects of tree- and one-loop diagrams involving 5D gluon and Higgs exchanges
as well as QCD corrections arising from the evolution from the Kaluza-Klein
scale to the typical scale of the decay. We find the RS corrections to the
branching fraction can be sizeable for large Yukawas and moderate KK scales
; for small Yukawas the RS contribution is small enough to be invisible in
current experimental data.Comment: 20 pages, 5 figures(V2: references added, matches version published
in Nuclear Physics B
The top-quark's running mass
We discuss the direct determination of the running top-quark mass from
measurements of the total cross section of hadronic top-quark pair-production.
The theory predictions in the MSbar scheme are very stable under scale
variations and show rapid apparent convergence of the perturbative expansion.
These features are explained by studying the underlying parton dynamics.Comment: 6 pages, 2 figures; to appear in Proceedings of the 9th International
Symposium on Radiative Corrections, RADCOR 2009, Ascona, Switzerland, October
200
Lepton flavour violation in RS models with a brane- or nearly brane-localized Higgs
We perform a comprehensive study of charged lepton flavour violation in
Randall-Sundrum (RS) models in a fully 5D quantum-field-theoretical framework.
We consider the RS model with minimal field content and a "custodially
protected" extension as well as three implementations of the IR-brane localized
Higgs field, including the non-decoupling effect of the Kaluza-Klein (KK)
excitations of a narrow bulk Higgs. Our calculation provides the first complete
result for the flavour-violating electromagnetic dipole operator in
Randall-Sundrum models. It contains three contributions with different
dependence on the magnitude of the anarchic 5D Yukawa matrix, which can all be
important in certain parameter regions. We study the typical range for the
branching fractions of mu -> e gamma, mu -> 3e, mu N -> e N as well as tau ->
mu gamma, tau -> 3 mu and the electron electric dipole moment by a numerical
scan in both the minimal and the custodial RS model. The combination of mu -> e
gamma and mu N -> e N currently provides the most stringent constraint on the
parameter space of the model. A typical lower limit on the KK scale T is around
2 TeV in the minimal model (up to 4 TeV in the bulk Higgs case with large
Yukawa couplings), and around 4 TeV in the custodially protected model, which
corresponds to a mass of about 10 TeV for the first KK excitations, far beyond
the lower limit from the non-observation of direct production at the LHC.Comment: 64 pages, 21 figures, LaTeX, v2: electron EDM analysis added, matches
published versio
- XSummer - Transcendental Functions and Symbolic Summation in Form
Harmonic sums and their generalizations are extremely useful in the
evaluation of higher-order perturbative corrections in quantum field theory. Of
particular interest have been the so-called nested sums,where the harmonic sums
and their generalizations appear as building blocks, originating for example
from the expansion of generalized hypergeometric functions around integer
values of the parameters. In this Letter we discuss the implementation of
several algorithms to solve these sums by algebraic means, using the computer
algebra system Form.Comment: 21 pages, 1 figure, Late
Scattering amplitudes for e^+e^- --> 3 jets at next-to-next-to-leading order QCD
We present the calculation of the fermionic contribution to the QCD two-loop
amplitude for e^+e^- --> q qbar g.Comment: 5 pages, 4 figures, espcrc2.sty (included), Talk given at QCD '02,
Montpellier, France, 2-9th July 200
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