795 research outputs found
On the Unification of Gauge Symmetries in Theories with Dynamical Symmetry Breaking
We analyze approaches to the partial or complete unification of gauge
symmetries in theories with dynamical symmetry breaking. Several types of
models are considered, including those that (i) involve sufficient unification
to quantize electric charge, (ii) attempt to unify the three standard-model
gauge interactions in a simple Lie group that forms a direct product with an
extended technicolor group, and, most ambitiously, (iii) attempt to unify the
standard-model gauge interactions with (extended) technicolor in a simple Lie
group.Comment: 24 pages, ReVTe
Implications of Dynamical Generation of Standard-Model Fermion Masses
We point out that if quark and lepton masses arise dynamically, then in a
wide class of theories the corresponding running masses exhibit
the power-law decay for Euclidean momenta
, where is a fermion of generation , and
is the maximal scale relevant for the origin of . We estimate
resultant changes in precision electroweak quantities and compare with current
data. It is found that this data allows the presence of such corrections. We
also note that this power-law decay renders primitively divergent fermion mass
corrections finite.Comment: 4 pages, late
Pair Production of MSSM Higgs Bosons in the Non-decoupling Region at the LHC
We consider the Higgs boson signals from pair production at the LHC within
the framework of the MSSM in the non-decoupling (low-m_A) region. In light of
the recent observation of a SM-like Higgs boson, we argue that the exploration
for Higgs pair production at the LHC is a crucial next step to probe the MSSM
Higgs sector. We emphasize that the production of H^\pm A^0 and H^{+}H^{-}
depends only on the electroweak gauge couplings while all the leading Higgs
production channels via gluon fusion, vector-boson fusion, and Higgsstrahlung
depend on additional free Higgs sector parameters. In the non-decoupling
region, the five MSSM Higgs bosons are all relatively light and pair production
signals may be accessible. We find that at the 8 TeV LHC, a 5\sigma signal for
H^\pm A^0, H^\pm h^0 -> \tau^{\pm}\nu b\bar b and H^{+}H^{-} -> \tau^{+}\nu
\tau^{-}\nu are achievable with an integrated luminosity of 7 (11) fb^{-1} and
24 (48) fb^{-1}, respectively for m_A=95 (130) GeV. At the 14 TeV LHC, a
5\sigma signal for these two channels would require as little as 4 (7) fb^{-1}
and 10 (19) fb^{-1}, respectively.Comment: 20 pages, 8 figures and 3 tables. Version to appear in PR
Deconstructed Higgsless Models at LHC: The Top Triangle Moose
We describe a deconstructed Higgsless model in which electroweak symmetry
breaking results largely from a Higgsless mechanism while the top quark mass is
generated by a topcolor mechanism. The top quark mass arises from a Yukawa
coupling to an effective top-Higgs which develops a small vacuum expectation
value. Both the heavy partners of the electoweak gauge bosons and those for the
SM fermions can be light enough to be visible at LHC.Comment: 5 pages, 3 figures; from the Proceedings of the 2010 Rencontres de
Bloi
Extended Technicolor Models with Two ETC Groups
We construct extended technicolor (ETC) models that can produce the large
splitting between the masses of the and quarks without necessarily
excessive contributions to the parameter or to neutral flavor-changing
processes. These models make use of two different ETC gauge groups, such that
left- and right-handed components of charge quarks transform under the
same ETC group, while left- and right-handed components of charge -1/3 quarks
and charged leptons transform under different ETC groups. The models thereby
suppress the masses and relative to , and and
relative to because the masses of the quarks and charged leptons
require mixing between the two ETC groups, while the masses of the
quarks do not. A related source of the differences between these mass
splittings is the effect of the two hierarchies of breaking scales of the two
ETC groups. We analyze a particular model of this type in some detail. Although
we find that this model tends to suppress the masses of the first two
generations of down-type quarks and charged leptons too much, it gives useful
insights into the properties of theories with more than one ETC group.Comment: 14 pages, 4 figure
New developments in FeynRules
The program FeynRules is a Mathematica package developed to facilitate the
implementation of new physics theories into high-energy physics tools. Starting
from a minimal set of information such as the model gauge symmetries, its
particle content, parameters and Lagrangian, FeynRules provides all necessary
routines to extract automatically from the Lagrangian (that can also be
computed semi-automatically for supersymmetric theories) the associated Feynman
rules. These can be further exported to several Monte Carlo event generators
through dedicated interfaces, as well as translated into a Python library,
under the so-called UFO model format, agnostic of the model complexity,
especially in terms of Lorentz and/or color structures appearing in the
vertices or of number of external legs. In this work, we briefly report on the
most recent new features that have been added to FeynRules, including full
support for spin-3/2 fermions, a new module allowing for the automated
diagonalization of the particle spectrum and a new set of routines dedicated to
decay width calculations.Comment: 6 pages. Contribution to the 15th International Workshop on advanced
computing and analysis techniques (ACAT 2013), 16-21 May, Beijing, Chin
Low-Energy Effective Theory, Unitarity, and Non-Decoupling Behavior in a Model with Heavy Higgs-Triplet Fields
We discuss the properties of a model incorporating both a scalar electroweak
Higgs doublet and an electroweak Higgs triplet. We construct the low-energy
effective theory for the light Higgs-doublet in the limit of small (but
nonzero) deviations in the rho parameter from one, a limit in which the triplet
states become heavy. For small deviations in the rho parameter from one,
perturbative unitarity of WW scattering breaks down at a scale inversely
proportional to the renormalized vacuum expectation value of the triplet field
(or, equivalently, inversely proportional to the square-root of the deviation
of the rho parameter from one). This result imposes an upper limit on the
mass-scale of the heavy triplet bosons in a perturbative theory; we show that
this upper bound is consistent with dimensional analysis in the low-energy
effective theory. Recent articles have shown that the triplet bosons do not
decouple, in the sense that deviations in the rho parameter from one do not
necessarily vanish at one-loop in the limit of large triplet mass. We clarify
that, despite the non-decoupling behavior of the Higgs-triplet, this model does
not violate the decoupling theorem since it incorporates a large dimensionful
coupling. Nonetheless, we show that if the triplet-Higgs boson masses are of
order the GUT scale, perturbative consistency of the theory requires the
(properly renormalized) Higgs-triplet vacuum expectation value to be so small
as to be irrelevant for electroweak phenomenology.Comment: Revtex, 11 pages, 7 eps figures included; references updated and
three footnotes adde
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