553 research outputs found
Measuring CP violation in Two-Higgs-Doublet models in light of the LHC Higgs data
In Two-Higgs-Doublet models, the conditions for CP violation can be expressed
in terms of invariants under U(2) rotations among the two SU(2) Higgs doublet
fields. In order to design a strategy for measuring the invariants we express
them in terms of observables, i.e., masses and couplings of scalar bosons. We
find amplitudes directly sensitive to the invariants. Observation of the
Standard-Model-like Higgs boson at the LHC severely constrains the models. In
particular, in the model with Z_2 symmetry imposed on dimension-4 terms (in
order to eliminate tree-level flavour-changing neutral currents), CP violation
is strongly suppressed. On the other hand, the most general Two-Higgs-Doublet
model (without Z_2 symmetry) would still allow for CP violation to be present
in the model, without being in conflict with the LHC data. Consequently, also
flavour-changing neutral currents would in general be expected. We briefly
sketch a strategy for measuring the remaining CP violation.Comment: 26 pages, 7 figures. Version published in JHE
Testing the presence of CP violation in the 2HDM
We review CP properties of the Two-Higgs-Doublet model. In particular, we
show that spontaneous CP violation occurs in the parameter space on the border
between regions allowing explicit CP violation and those where there is another
minimum, deeper than the one corresponding to v=246 GeV. We discuss weak-basis
invariants which describe CP violation and express them through measurable
quantities like coupling constants and masses. Also, we discuss how CP
violation is constrained by the LHC Higgs data. Finally, we identify effective
operators that could be adopted to measure CP-invariants.Comment: 9 pages, Proceedings of the Corfu Summer Institute 2014 "School and
Workshops on Elementary Particle Physics and Gravity", 3-21 September 2014
Corfu, Greece. v2: References adde
Diagnosing CP properties of the 2HDM
We have investigated a Two-Higgs-Doublet Model (2HDM), focusing on CP
violation. Various scenarios with spontaneous and explicit breaking of CP have
been considered. Some features of CP violation related to a choice of the basis
for the two Higgs doublets have been discussed and clarified. Regions in the
physical parameter space corresponding to spontaneous and explicit CP violation
have been located and discussed. The possibility to determine parameters of the
scalar potential with no reference to Yukawa couplings has been considered and
an unavoidable ambiguity has been found. The issue of disentangling spontaneous
and explicit CP violation has been investigated.Comment: 32 pages, 5 figures. Minor changes. Version to appear in JHE
Update on the CP-Violating Inert-Doublet Model
We have updated a recently proposed extension of the Inert Doublet Model. The
extension amounts to the addition of an extra non-inert scalar doublet. The
model thus offers a possibility of CP violation in the scalar sector and a
candidate for the Dark Matter. The recent XENON100 direct-detection experiment
excludes a considerable range of medium-low dark-matter masses, leaving only as
viable very low masses of order 5-10 GeV, as well as the regions from \sim 60
to \sim 110 GeV, and above \sim 530 GeV. For favorable parameter regions one
may observe related long-lived charged particles produced at the LHC.Comment: Contribution to PoS Proceedings, The XXth International Workshop High
Energy Physics and Quantum Field Theory, September 24 - October 1, 2011,
Sochi, Russi
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
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
H/A Higgs Mixing in CP-Noninvariant Supersymmetric Theories
For large masses, the two heavy neutral Higgs bosons are nearly degenerate in
many 2--Higgs doublet models, and particularly in supersymmetric models. In
such a scenario the mixing between the states can be very large if the theory
is CP-noninvariant. We analyze the formalism describing this configuration, and
we point to some interesting experimental consequences.Comment: LaTeX, 1+20 pages, 6 figure
New results for a photon-photon collider
We present new results from studies in progress on physics at a two-photon
collider. We report on the sensitivity to top squark parameters of MSSM Higgs
boson production in two-photon collisions; Higgs boson decay to two photons;
radion production in models of warped extra dimensions; chargino pair
production; sensitivity to the trilinear Higgs boson coupling; charged Higgs
boson pair production; and we discuss the backgrounds produced by resolved
photon-photon interactions.Comment: 17 pages, 15 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
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