428 research outputs found
CP Nonconservation in at the Tevatron
The reaction is found to be rather rich in exhibiting
several different types of CP asymmetries. The spin of the top quark plays an
important role. Asymmetries are related to form factors arising from radiative
corrections of the production vertex due to non-standard physics. As
illustrations, effects are studied in two Higgs Doublet Models and in
Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that
appeared on some postscript previewers. No change in conten
Dimension-Six Terms in the Standard Model Lagrangian
When the Standard Model is considered as an effective low-energy theory,
higher dimensional interaction terms appear in the Lagrangian. Dimension-six
terms have been enumerated in the classical article by Buchmueller and Wyler
[3]. Although redundance of some of those operators has been already noted in
the literature, no updated complete list has been published to date. Here we
perform their classification once again from the outset. Assuming baryon number
conservation, we find 15 + 19 + 25 = 59 independent operators (barring flavour
structure and Hermitian conjugations), as compared to 16 + 35 + 29 = 80 in
Ref.[3]. The three summed numbers refer to operators containing 0, 2 and 4
fermion fields. If the assumption of baryon number conservation is relaxed, 4
new operators arise in the four-fermion sector.Comment: 16 pages, no figures, v3: Redundant B-violating operator remove
Top effective operators at the ILC
We investigate the effect of top trilinear operators in t tbar production at
the ILC. We find that the sensitivity to these operators largely surpasses the
one achievable by the LHC either in neutral or charged current processes,
allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy
of 500 GeV. We show how the use of beam polarisation and an eventual energy
upgrade to 1 TeV allow to disentangle all effective operator contributions to
the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE
Top effective operators at the ILC
We investigate the effect of top trilinear operators in t tbar production at
the ILC. We find that the sensitivity to these operators largely surpasses the
one achievable by the LHC either in neutral or charged current processes,
allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy
of 500 GeV. We show how the use of beam polarisation and an eventual energy
upgrade to 1 TeV allow to disentangle all effective operator contributions to
the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE
Large Tree Level CP Violation in in The Two Higgs Doublet Model
We find a large CP violation effect within the Two-Higgs-Doublet-Model for
the reaction at future linear colliders. The
CP-asymmetry arises already at the tree level as a result of interference
between diagrams with emission from (and ) and its emission
from a and can be about 10--20\%. In the best case one needs a few
hundred events to observe CP violation at the 3 level.Comment: UU encoded tar compressed tex file with postscript figure
Multi-Scalar-Singlet Extension of the Standard Model - the Case for Dark Matter and an Invisible Higgs Boson
We consider a simple extension of the Standard Model by the addition of N
real scalar gauge singlets \vp that are candidates for Dark Matter. By
collecting theoretical and experimental constraints we determine the space of
allowed parameters of the model. The possibility of ameliorating the little
hierarchy problem within the multi-singlet model is discussed. The
Spergel-Steinhardt solution of the Dark Matter density cusp problem is
revisited. It is shown that fitting the recent CRESST-II data for Dark Matter
nucleus scattering implies that the standard Higgs boson decays predominantly
into pairs of Dark Matter scalars. It that case discovery of the Higgs boson at
LHC and Tevatron is impossible. The most likely mass of the dark scalars is in
the range 15 GeV \lsim \mvp \lsim 50 GeV with BR(h \to \vp\vp) up to 96%.Comment: 18 pages, 15 figure
Study of CP Property of the Higgs at a Photon Collider using
We study possible effects of CP violation in the Higgs sector on
production at a -collider. These studies are performed in a
model-independent way in terms of six form-factors which
parametrize the CP mixing in the Higgs sector, and a strategy for their
determination is developed. We observe that the angular distribution of the
decay lepton from produced in this process is independent of any CP
violation in the vertex and hence best suited for studying CP mixing in
the Higgs sector. Analytical expressions are obtained for the angular
distribution of leptons in the c.m. frame of the two colliding photons for a
general polarization state of the incoming photons. We construct combined
asymmetries in the initial state lepton (photon) polarization and the final
state lepton charge. They involve CP even ('s) and odd ('s) combinations
of the mixing parameters. We study limits up to which the values of and
, with only two of them allowed to vary at a time, can be probed by
measurements of these asymmetries, using circularly polarized photons. We use
the numerical values of the asymmetries predicted by various models to
discriminate among them. We show that this method can be sensitive to the
loop-induced CP violation in the Higgs sector in the MSSM.Comment: 15 pages, 9 figures added one referenc
Weak Mixing Angle and Higgs Mass in Gauge-Higgs Unification Models with Brane Kinetic Terms
We show that the idea of Gauge-Higgs unification(GHU) can be rescued from the
constraint of weak mixing angle by introducing localized brane kinetic terms in
higher dimensional GHU models with bulk and simple gauge groups. We find that
those terms lead to a ratio between Higgs and W boson masses, which is a little
bit deviated from the one derived in the standard model. From numerical
analysis, we find that the current lower bound on the Higgs mass tends to
prefer to exceptional groups E(6), E(7), E(8) rather than other groups like
SU(3l), SO(2n+1), G(2), and F(4) in 6-dimensional(D) GHU models irrespective of
the compactification scales. For the compactification scale below 1 TeV, the
Higgs masses in 6D GHU models with SU(3l), SO(2n+1), G(2), and F(4) groups are
predicted to be less than the current lower bound unless a model parameter
responsible for re-scaling SU(2) gauge coupling is taken to be unnaturally
large enough. To see how the situation is changed in more higher dimensional
GHU model, we take 7D S^{3}/ Z_{2} and 8D T^{4}/ Z_{2} models. It turns out
from our numerical analysis that these higher dimensional GHU models with gauge
groups except for E(6) can lead to the Higgs boson whose masses are predicted
to be above the current lower bound only for the compatification scale above 1
TeV without taking unnaturally large value of the model parameter, whereas the
Higgs masses in the GHU models with E(6) are compatible with the current lower
bound even for the compatification scale below 1 TeV.Comment: 22 pages, 4 figure
A review of Quantum Gravity at the Large Hadron Collider
The aim of this article is to review the recent developments in the
phenomenology of quantum gravity at the Large Hadron Collider. We shall pay
special attention to four-dimensional models which are able to lower the
reduced Planck mass to the TeV region and compare them to models with a large
extra-dimensional volume. We then turn our attention to reviewing the emission
of gravitons (massless or massive) at the LHC and to the production of small
quantum black holes.Comment: 32 pages, invited revie
Electroweak symmetry breaking and radion stabilization in universal extra dimensions
We discuss the stabilization of the scalar sector, including the radion, in
the gauge model with one universal extra dimension, within Higgs and Higgsless
scenarios. The stabilization occurs at the one-loop level, through the
fermionic contribution to the effective potential; in the Higgs case, for
stabilization to take place the bosonic contribution must be balanced by the
fermionic one, hence the scales of these two cannot differ too much. However,
there is no need for (softly broken) supersymmetry to achieve the stabilization
- it can be arranged for a reasonably wide range of couplings and mass scales.
The primary instability in the model is the run-away of the radion vacuum
expectation value. It turns out that the requirement of the radion stability,
in the Higgs case, favours a Higgs boson mass below 0.26 TeV, which is
consistent with the Standard Model upper bound that follows from the
electroweak precision measurements. The typical radion mass is of the order of
10^{-6} eV. The radion mass can be made larger by rising the scale of fermion
masses, as clearly seen in the Higgsless case. The cosmological constant may be
cancelled by suitable counterterms, in such a way that the stabilization is not
affected.Comment: 20 pages, 2 figures, references adde
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