642 research outputs found
Natural fourth generation of leptons
We consider implications of a fourth generation of leptons, allowing for the
most general mass patterns for the fourth generation neutrino. We determine the
constraints due to the precision electroweak measurements and outline the
signatures to search for at the LHC experiments. As a concrete framework to
apply these results we consider the minimal walking technicolor (MWTC) model
where the matter content, regarding the electroweak quantum numbers,
corresponds to a fourth generation.Comment: 21 pages, 11 figures, 1 table; version to appear in JHE
Pressure to order in -theory at weak coupling
We calculate the pressure of massless -theory to order
at weak coupling. The contributions to the pressure arise from the hard
momentum scale of order and the soft momentum scale of order .
Effective field theory methods and dimensional reduction are used to separate
the contributions from the two momentum scales: The hard contribution can be
calculated as a power series in using naive perturbation theory with bare
propagators. The soft contribution can be calculated using an effective theory
in three dimensions, whose coefficients are power series in . This
contribution is a power series in starting at order . The calculation
of the hard part to order involves a complicated four-loop sum-integral
that was recently calculated by Gynther, Laine, Schr\"oder, Torrero, and
Vuorinen. The calculation of the soft part requires calculating the mass
parameter in the effective theory to order and the evaluation of
five-loop vacuum diagrams in three dimensions. This gives the free energy
correct up to order . The coefficients of the effective theory satisfy a
set of renormalization group equations that can be used to sum up leading and
subleading logarithms of . We use the solutions to these equations to
obtain a result for the free energy which is correct to order .
Finally, we investigate the convergence of the perturbative series.Comment: 29 pages and 12 figs. New version: we have pushed the calculations to
g^8*log(g) using the renormalization group to sum up log(g) from higher
orders. Published in JHE
The Electroweak Phase Transition in Ultra Minimal Technicolor
We unveil the temperature-dependent electroweak phase transition in new
extensions of the Standard Model in which the electroweak symmetry is
spontaneously broken via strongly coupled, nearly-conformal dynamics achieved
by the means of multiple matter representations. In particular, we focus on the
low energy effective theory introduced to describe Ultra Minimal Walking
Technicolor at the phase transition. Using the one-loop effective potential
with ring improvement, we identify regions of parameter space which yield a
strong first order transition. A striking feature of the model is the existence
of a second phase transition associated to the electroweak-singlet sector. The
interplay between these two transitions leads to an extremely rich phase
diagram.Comment: 38 RevTeX pages, 9 figure
Minimal Flavor Constraints for Technicolor
We analyze the constraints on the the vacuum polarization of the standard
model gauge bosons from a minimal set of flavor observables valid for a general
class of models of dynamical electroweak symmetry breaking. We will show that
the constraints have a strong impact on the self-coupling and masses of the
lightest spin-one resonances. Our analysis is applicable to any four and higher
dimensional extension of the standard model reducing to models of dynamical
electroweak symmetry breaking.Comment: 26 pages, we have added appendix C and some references and corrected
some typo
Constraints on Conformal Windows from Holographic Duals
We analyze a beta function with the analytic form of
Novikov-Shifman-Vainshtein-Zakharov result in the five dimensional
gravity-dilaton environment. We show how dilaton inherits poles and fixed
points of such beta function through the zeros and points of extremum in its
potential. Super Yang-Mills and supersymmetric QCD are studied in detail and
Seiberg's electric-magnetic duality in the dilaton potential is explicitly
demonstrated. Non-supersymmetric proposals of similar functional form are
tested and new insights into the conformal window as well as determinations of
scheme-independent value of the anomalous dimension at the fixed point are
presented.Comment: Fig. 5b is corrected to match the discussion in the tex
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