15,138 research outputs found
Unitarity of the Higher Dimensional Standard Model
We study the unitarity of the standard model (SM) in higher dimensions. We
show that the essential features of SM unitarity remain after compactification,
and place bounds on the highest Kaluza-Klein (KK) level N_KK and the Higgs mass
m_H in the effective four-dimensional (4d) low-energy theory. We demonstrate
these general observations by explicitly analyzing the effective 4d KK theory
of a compactified 5d SM on S^1/Z_2. The nontrivial energy cancellations in the
scattering of longitudinal KK gluons or KK weak bosons, a consequence of the
geometric Higgs mechanism, are verified. In the case of the electroweak gauge
bosons, the longitudinal KK states also include a small mixture from the KK
Higgs excitations. With the analyses before and after compactification, we
derive the strongest bounds on N_KK from gauge KK scattering. Applying these
bounds to higher-dimensional SUSY GUTs implies that only a small number of KK
states can be used to accelerate gauge coupling unification. As a consequence,
we show that the GUT scale in the 5d minimal SUSY GUT cannot be lower than
about 10^{14} GeV.Comment: Version in Phys. Lett. B (minor typos fixed, refs added
Dynamical CP Violation in Composite Higgs Models - a Review -
In composite Higgs models it was pointed out that there is a possibility to
violate CP symmetry dynamically. We demonstrated a simple model of dynamical CP
violation in composite Higgs models. We calculated the neutron electric dipole
moment in our model and the constraint for our model is discussed. (Talk
presented at the Third KEK Topical Conference on CP Violation, 16-18 November,
1993. The main part of this talk is based on the work in collaboration with S.
Hashimoto and T. Muta.)Comment: 14 pages, 2 figures not included, uses LaTeX, HUPD-940
Flavorful signatures at LHC and ILC
There are lots of new physics models which predict an extra neutral gauge
boson, referred as Z'-boson. In a certain class of these new physics models,
the Z'-boson has flavor-dependent couplings with the fermions in the Standard
Model (SM). Based on a simple model in which couplings of the SM fermions in
the third generation with the Z'-boson are different from those of the
corresponding fermions in the first two generations, we study the signatures of
Z'-boson at the Large Hadron Collider (LHC) and the International Linear
Collider (ILC). We show that at the LHC, the Z'-boson with mass around 1 TeV
can be produced through the Drell-Yan processes and its dilepton decay modes
provide us clean signatures not only for the resonant production of Z'-boson
but also for flavor-dependences of the production cross sections. We also study
fermion pair productions at the ILC involving the virtual Z'-boson exchange.
Even though the center-of-energy of the ILC is much lower than a Z'-boson mass,
the angular distributions and the forward-backward asymmetries of fermion pair
productions show not only sizable deviations from the SM predictions but also
significant flavor-dependences.Comment: 11 pages, 5 figures, some typos corrected, the version to appear in
PL
Production of the top-pions at the THERA collider based collisions
In the framework of the topcolor-assisted technicolor (TC2) models, we study
the production of the top-pions , via the
processes and
mediated by the anomalous top coupling . We find that the production
cross section of the process is very small. With
reasonable values of the parameters in TC2 models, the production cross section
of the process can reach . The charged
top-pions might be directly observed via this process at the
THERA collider based collisions.Comment: 10 pages, 3 figure
Unitarity of Compactified Five Dimensional Yang-Mills Theory
Compactified five dimensional Yang-Mills theory results in an effective
four-dimensional theory with a Kaluza-Klein (KK) tower of massive vector
bosons. We explicitly demonstrate that the scattering of the massive vector
bosons is unitary at tree-level for low energies, and analyze the relationship
between the unitarity violation scale in the KK theory and the
nonrenormalizability scale in the five dimensional gauge theory. In the
compactified theory, low-energy unitarity is ensured through an interlacing
cancellation among contributions from the relevant KK levels. Such
cancellations can be understood using a Kaluza-Klein equivalence theorem which
results from the geometric ``Higgs'' mechanism of compactification. In these
theories, the unitarity violation is delayed to energy scales higher than the
customary limit through the introduction of additional vector bosons rather
than Higgs scalars.Comment: 10 pages, 1 eps figure, discussion of deconstruction expanded,
version accepted for publication in PL
Anomalous Gauge Interactions of the Higgs Boson: Precision Constraints and Weak Boson Scatterings
Interaction of Higgs scalar (H) with weak gauge bosons (V=W,Z) is the {\it
key} to understand electroweak symmetry breaking (EWSB) mechanism. New physics
effects in the HVV interactions, as predicted by models of compositeness,
supersymmetry and extra dimensions, can be formulated as anomalous couplings
via a generic effective Lagrangian. We first show that the existing electroweak
precision data already impose nontrivial indirect constraints on the anomalous
HVV couplings. Then, we systematically study VV --> VV scatterings in the TeV
region, via Gold-plated pure leptonic decay modes of the weak bosons. We
demonstrate that, even for a light Higgs boson in the mass range 115GeV < m_H <
300GeV, this process can directly probe the anomalous HVV interactions at the
LHC with an integrated luminosity of 300fb^{-1}, which further supports the
``No-Lose'' theorem for the LHC to uncover the EWSB mechanism. Comparisons with
the constraints from measuring the cross section of VH associate production and
the Higgs boson decay width are also given.Comment: Version in Phys. Lett. B (v3: minor typos removed, v2,v4: fix Latex
top-margin
Natural Theories of Ultra-Low Mass PNGB's: Axions and Quintessence
We consider the Wilson Line PNGB which arises in a U(1)^N gauge theory,
abstracted from a latticized, periodically compactified extra dimension U(1).
Planck scale breaking of the PNGB's global symmetry is suppressed, providing
natural candidates for the axion and quintessence. We construct an explicit
model in which the axion may be viewed as the 5th component of the U(1)_Y gauge
field in a 1+4 latticized periodically compactified extra dimension. We also
construct a quintessence PNGB model where the ultra-low mass arises from
Planck-scale suppressed physics itself.Comment: 20 pages, fixed typo and reference
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