2,009 research outputs found
New Renormalization Group Equations and the Naturalness Problem
Looking for an observable manifestation of the so-called unnaturalness of
scalar fields we introduce a seemingly new set of differential equations for
connected Green functions. These equations describe the momentum dependence of
the Green functions and are close relatives to the previously known
renormalization group equations. Applying the new equations to the theory of
scalar field with interaction we identify a relation between the
four-point Green function and the propagator which expresses the unnaturalness
of the scalar field. Possible manifestations of the unnaturalness at low
momenta are briefly discussed.Comment: 12 revtex pages; a coefficient has been corrected in eq. (34), four
new references added; final version to appear in Phys. Rev.
Off-Shell Scattering Amplitudes for WW Scattering and the Role of the Photon Pole
We derive analytic expressions for high energy off-shell scattering
amplitudes of weak vector bosons. They are obtained from six fermion final
states in processes of the type . As an application we reconsider the
unitarity bounds on the Higgs mass. Particular attention is given to the role
of the photon exchange which has not been considered in earlier investigations;
we find that the photon weakens the bound of the Higgs mass.Comment: 16 pages, 8 figure
Boosting Higgs discovery - the forgotten channel
Searches for a heavy Standard Model Higgs boson focus on the 'gold plated
mode' where the Higgs decays to two leptonic Z bosons. This channel provides a
clean signature, in spite of the small leptonic branching ratios. We show that
using fat jets the semi-leptonic ZZ mode significantly increases the number of
signal events with a similar statistical significance as the leptonic mode.Comment: 12 pages, 3 figure
The unit of electric charge and the mass hierarchy of heavy particles
We propose some empirical formulae relating the masses of the heaviest
particles in the standard model (the W,Z,H bosons and the t quark) to the
charge of the positron and the Higgs condensate v. The relations for the
masses of gauge bosons m_W = (1+e)v/4 and m_Z=sqrt{(1+e^2)/2}*(v/2) are in
excellent agreement with experimental values. By requiring the electroweak
standard model to be free from quadratic divergencies at the one-loop level, we
find: m_t=v/sqrt{2} and m_H=v/sqrt{2e}, or the very simple ratio (m_t/m_H)^2=e.Comment: 6 page
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
Dropping rho and A_1 Meson Masses at Chiral Phase Transition in the Generalized Hidden Local Symmetry
We study the chiral symmetry restoration using the generalized hidden local
symmetry (GHLS) which incorporates the rho and A_1 mesons as the gauge bosons
of the GHLS and the pion as the Nambu-Goldstone boson consistently with the
chiral symmetry of QCD. We show that a set of parameter relations, which
ensures the first and second Weinberg's sum rules, is invariant under the
renormalization group evolution. Then, we found that the Weinberg's sum rules
together with the matching of the vector and axial-vector current correlators
inevitably leads to {\it the dropping masses of both rho and A_1 mesons} at the
symmetry restoration point, and that the mass ratio as well as the mixing angle
between the pion and A_1 meson flows into one of three fixed points.Comment: 17 pages, 7 figures; references added and discussions expande
Constraints on the excitations in the Strongly Coupled Standard Model
The Strongly Coupled Standard Model predicts a rich spectrum of excited
states at the Fermi scale. We study the first radial excitations of the vector
bosons. The inclusion of these new states affects the low energy phenomenology
of the model. We put constraints on the effective couplings by performing a
global fit with the electroweak observables, and we find that the excitations
have to be rather decoupled from the low-energy states.Comment: 23 pages, 6 figures, uses RevTeX
Supersymmetric NLO QCD Corrections to Resonant Slepton Production and Signals at the Tevatron and the LHC
We compute the total cross section and the transverse momentum distribution
for single charged slepton and sneutrino production at hadronic colliders
including NLO supersymmetric and non-supersymmetric QCD corrections. The
supersymmetric QCD corrections can be substantial. We also resum the gluon
transverse momentum distribution and compare our results with two Monte Carlo
generators. We compute branching ratios of the supersymmetric decays of the
slepton and determine event rates for the like-sign dimuon final state at the
Tevatron and at the LHC.Comment: 14 pages, LaTeX, 8 figures, uses REVTex
What is the discrete gauge symmetry of the R-parity violating MSSM?
The lack of experimental evidence for supersymmetry motivates R-parity
violating realizations of the MSSM. Dropping R-parity, alternative symmetries
have to be imposed in order to stabilize the proton. We determine the possible
discrete R and non-R symmetries, which allow for renormalizable R-parity
violating terms in the superpotential and which, at the effective level, are
consistent with the constraints from nucleon decay. Assuming a gauge origin, we
require the symmetry to be discrete gauge anomaly-free, allowing also for
cancellation via the Green Schwarz mechanism. Furthermore, we demand lepton
number violating neutrino mass terms either at the renormalizable or
non-renormalizable level. In order to solve the mu problem, the discrete Z_N or
Z_N^R symmetries have to forbid any bilinear superpotential operator at tree
level. In the case of renormalizable baryon number violation the smallest
possible symmetry satisfying all conditions is a unique hexality Z_6^R. In the
case of renormalizable lepton number violation the smallest symmetries are two
hexalities, one Z_6 and one Z_6^R.Comment: 25 pages, version to appear in PR
Two-photon exchange in elastic electron-nucleon scattering
A detailed study of two-photon exchange in unpolarized and polarized elastic
electron--nucleon scattering is presented, taking particular account of nucleon
finite size effects. Contributions from nucleon elastic intermediate states are
found to have a strong angular dependence, which leads to a partial resolution
of the discrepancy between the Rosenbluth and polarization transfer
measurements of the proton electric to magnetic form factor ratio, G_E/G_M. The
two-photon exchange contribution to the longitudinal polarization transfer P_L
is small, whereas the contribution to the transverse polarization transfer P_T
is enhanced at backward angles by several percent, increasing with Q^2. This
gives rise to a small, ~3% suppression of G_E/G_M obtained from the
polarization transfer ratio P_T/P_L at large Q^2. We also compare the
two-photon exchange effects with data on the ratio of e^+ p to e^- p cross
sections, which is predicted to be enhanced at backward angles. Finally, we
evaluate the corrections to the form factors of the neutron, and estimate the
elastic intermediate state contribution to the ^3He form factors
- …