117 research outputs found
Electroweak Precision Tests: A Concise Review
1. Introduction 2. Status of the Data 3. Precision Electroweak Data and the
Standard Model 4. A More General Analysis of Electroweak Data
4.1 Basic Definitions and Results
4.2 Experimental Determination of the Epsilon Variables
4.3 Comparing the Data with the Minimal Supersymmetric Standard Model 5.
Theoretical Limits on the Higgs Mass 6. ConclusionComment: Submitted to Int. Journal of Modern Physics
Indication for Light Sneutrinos and Gauginos from Precision Electroweak Data
The present Standard Model fit of precision data has a low confidence level,
and is characterized by a few inconsistencies. We look for supersymmetric
effects that could improve the agreement among the electroweak precision
measurements and with the direct lower bound on the Higgs mass. We find that
this is the case particularly if the 3.6 sigma discrepancy between sin^2
theta_eff from leptonic and hadronic asymmetries is finally settled more on the
side of the leptonic ones. After the inclusion of all experimental constraints,
our analysis selects light sneutrinos, with masses in the range 55-80 GeV, and
charged sleptons with masses just above their experimental limit, possibly with
additional effects from light gauginos. The phenomenological implications of
this scenario are discussed.Comment: 17 pages LaTex, 9 figures, uses epsfi
Gauge boson families in grand unified theories of fermion masses: E_6^4 x S_4
In third quantization the origin of fermion families is easy to understand:
the electron field, the muon field and the tau field are identical fields in
precisely the same sense as three electrons are identical and undistinguishable
particles of a theory of second quantization. In both cases, the permutation of
these fields or particles leaves the lagrangian invariant. One can also extend
the concept of family to gauge bosons. This can be obtained through the
semidirect product of the gauge group with the group of permutations of n
objects. In this paper we have studied the group E_6^4 x S_4. We explain why we
have chosen E_6 as fundamental gauge group factor and why we start with a model
with four gauge boson/fermion families to accommodate and to fit the standard
model with only three fermion families. We suggest a possible symmetry breaking
pattern of E_6^4 x S_4 that could explain quark, lepton and neutrino masses and
mixings.Comment: 21 pages, no figur
Top-quark physics in six-quark final states at the Next Linear Collider
The processes of six-quark production with one pair are studied by
means of a complete tree-level electroweak calculation. The top-quark signal is
examined: the importance of electroweak backgrounds, of the order of 10% above
the threshold and of about 30% of the purely electroweak signal at
threshold, is further stressed by studying the dependence of the cross-section
at threshold on the Higgs mass in the range between 100 GeV and 185 GeV, and
finding variations of the order of 10%. In the study of some event-shape
variables, a strong effect of initial-state radiation is found, in particular
for the thrust distribution, which is studied for several centre-of-mass
energies at the TeV scale. The effectiveness of cuts on the thrust for
isolating QCD backgrounds, as pointed out by some authors, is confirmed also in
the presence of electroweak backgrounds and initial-state radiation.Comment: LaTeX (using elsart.sty), 17 pages, 9 figures include
Reconciling the LEP and Slac Measurements of Sin^2(\Theta_W)
We consider whether a discrepancy between the SLAC and LEP measurements of
\Sw can be explained by new physics. We find that only the contribution of a
new neutral gauge boson, , nearly degenerate with the Z can affect
the SLAC measurement while leaving the LEP observables almost unaffected. We
briefly discuss possible signals for this new gauge boson, including changes in
the lineshape when measured with polarised electrons, small changes in
, , and larger changes in two jet and production at
hadron colliders.Comment: 8 pages , CERN-TH.7474/94, OUTP9424
Impact of QED corrections to Higgs decay into four leptons at the LHC
At the LHC a precise measurement of the Higgs boson mass (if discovered), at
the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for
a wide range of Higgs mass values. To match such an accuracy, the systematic
effects induced by QED corrections need to be investigated. In the present
study the calculation of O(alpha) and higher order QED corrections is
illustrated as well as their impact on the Higgs mass determination, once
realistic event selection criteria for charged leptons and photons are
considered.Comment: 5 pages, 5 figures, 1 table. Presented at HEP2005 July 21st-27th,
2005, Lisboa, Portugal and at RADCOR 2005, Shonan Village, October 2nd-7th,
2005, Japa
A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4
We discuss a grand unified model based on SUSY SU(5) in extra dimensions and
on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing
for neutrinos with the accuracy required by the data, also leads to a natural
description of the observed pattern of quark masses and mixings.Comment: 19 page
Helac-Phegas: a generator for all parton level processes
The updated version of the Helac-Phegas event generator is presented. The
matrix elements are calculated through Dyson-Schwinger recursive equations.
Helac-Phegas generates parton-level events with all necessary information, in
the most recent Les Houches Accord format, for the study of any process within
the Standard Model in hadron and lepton colliders
Reduction formalism for dimensionally regulated one-loop N-point integrals
We consider one-loop scalar and tensor integrals with an arbitrary number of
external legs relevant for multi-parton processes in massless theories. We
present a procedure to reduce N-point scalar functions with generic
4-dimensional external momenta to box integrals in (4-2\epsilon) dimensions. We
derive a formula valid for arbitrary N and give an explicit expression for N=6.
Further a tensor reduction method for N-point tensor integrals is presented.
We prove that generically higher dimensional integrals contribute only to order
\epsilon for N>=5. The tensor reduction can be solved iteratively such that any
tensor integral is expressible in terms of scalar integrals. Explicit formulas
are given up to N=6.Comment: 21 pages Latex, 1 eps figur
On the computation of multigluon amplitudes
A computational algorithm based on recursive equations is developed in order
to estimate multigluon production processes at high energy hadron colliders.
The partonic reactions gg->(n-2)g with n up to n=9 are studied and comparisons
with known approximations are presented.Comment: 12 pages, LaTe
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