67 research outputs found
NNLO fermionic corrections to the charm quark mass dependent matrix elements in B -> X_s gamma
We compute the virtual O(alpha_s^2) fermionic contributions to the charm
quark mass dependent matrix elements of the B -> X_s gamma decay. In the case
of a massless quark loop insertion into the gluon propagator, our result
obtained as an expansion in z=m_c^2/m_b^2 and an exact expression in terms of
multi-fold MB integrals, confirms the findings of Bieri, Greub and Steinhauser
[19]. We observe, however, large deviations in the case of a b-quark loop
insertion.The charm quark loop shows smaller, but still noticeable differences.Comment: 11 pages, 3 figures, 1 tabl
Supersymmetric Contributions to Bs->K+K-
Inspired by the existing calculation of B->piK decays in supersymmetry
(SUSY), we evaluate the dominant SUSY contributions to Bs->K+K-. We show that
the observables of this process can be significantly modified in the presence
of SUSY. In particular, the branching ratio can be increased considerably
compared to the prediction of the standard model (SM). The effect is even more
dramatic for the CP-violating asymmetries A_dir and A_mix. These asymmetries,
expected to be small in the SM (A_dir is predicted to take only positive
values), change drastically with SUSY contributions. The measurement of these
observables can therefore be used to detect the presence of physics beyond the
SM, and put constraints on its parameters.Comment: 17 pages, 2 figures. This new version contains one added reference
and some minor style change
Transitions in Family-dependent Models
We analyze flavor-changing-neutral-current (FCNC) effects in the
transitions that are induced by family non-universal gauge symmetries.
After systematically developing the necessary formalism, we present a
correlated analysis for the processes. We adopt a
model-independent approach in which we only require family-universal charges
for the first and second generations and small fermion mixing angles. We
analyze the constraints on the resulting parameter space from
mixing and the time-dependent CP asymmetries of the penguin-dominated decays. Our results indicate that the
currently observed discrepancies in some of these modes with respect to the
Standard Model predictions can be consistently accommodated within this general
class of models.Comment: 36 pages, 11 figure
Prospects for the direct detection of neutralino dark matter in orbifold scenarios
We analyse the phenomenology of orbifold scenarios from the heterotic
superstring, and the resulting theoretical predictions for the direct detection
of neutralino dark matter. In particular, we study the parameter space of these
constructions, computing the low-energy spectrum and taking into account the
most recent experimental and astrophysical constraints, as well as imposing the
absence of dangerous charge and colour breaking minima. In the remaining
allowed regions the spin-independent part of the neutralino-proton cross
section is calculated and compared with the sensitivity of dark matter
detectors. In addition to the usual non universalities of the soft terms in
orbifold scenarios due to the modular weight dependence, we also consider
D-term contributions to scalar masses. These are generated by the presence of
an anomalous U(1), providing more flexibility in the resulting soft terms, and
are crucial in order to avoid charge and colour breaking minima. Thanks to the
D-term contribution, large neutralino detection cross sections can be found,
within the reach of projected dark matter detectors.Comment: 51 pages, 25 figure
Lepton non-universality at LEP and charged Higgs
A recent analysis of the LEP data shows an interesting deviation from lepton
universality in W boson decays. An excess at the level of 2.8 sigma is found in
the tau mode branching ratio with respect to the other two modes. It is
suggested that this seeming lepton non-universality might stem from pair
production of charged Higgs bosons almost degenerate with W, that
preferentially decay to heavy fermions. It is shown that the deviation can be
reduced to 1.4 sigma in two Higgs doublet model I without any conflict with the
existing direct or indirect constraints. This conclusion is largely independent
of tan beta, the ratio of Higgs vacuum expectation values. This scenario can be
tested at the forthcoming international linear collider.Comment: 16 pages, published version with minor change
Constraining the MSSM with universal gaugino masses and implication for searches at the LHC
Using a Markov chain Monte Carlo approach, we find the allowed parameter
space of a MSSM model with seven free parameters. In this model universality
conditions at the GUT scale are imposed on the gaugino sector. We require in
particular that the relic density of dark matter saturates the value extracted
from cosmological measurements assuming a standard cosmological scenario. We
characterize the parameter space of the model that satisfies experimental
constraints and illustrate the complementarity of the LHC searches, B-physics
observables and direct dark matter searches for further probing the parameter
space of the model. We also explore the different decay chains expected for the
coloured particles that would be produced at LHC.Comment: 29 pages, 11 figure
CP violation in the secluded U(1)'-extended MSSM
We study the Higgs sector of the secluded -extended MSSM (sMSSM)
focusing on CP violation. Using the one-loop effective potential that includes
contributions from quarks and squarks in the third generation, we search for
the allowed region under theoretical and experimental constraints. It is found
that the possible region for the electroweak vacuum to exist is quite limited,
depending on the parameters in the model. The masses and couplings of the Higgs
bosons are calculated with/without CP violation. Even at the tree level, CP
violation is possible by complex soft SUSY breaking masses. Similar to the CPX
scenario in the MSSM, the scalar-pseudoscalar mixing enables the lightest Higgs
boson mass to become smaller than the boson mass while the coupling with
the boson is sufficiently suppressed to avoid the LEP experimental
constraints. However, unlike the CPX scenario, large and are not
required for the realization of large CP violation. The typical spectrum of the
SUSY particles is thus different. We also investigate the possible upper bound
of the lightest Higgs boson in the case of spontaneous CP violation. The
maximal value of it can reach above 100 GeV with maximal CP-violating phases.Comment: 28 pages, 16 figures, JHEP styl
Footprints of the Beyond in flavor physics: Possible role of the Top Two Higgs Doublet Model
The B-factories results provide an impressive confirmation of the Standard
Model (SM) description of flavor and CP violation. Nevertheless, as more data
were accumulated, deviations in the 2.5-3.5 sigma range have emerged pointing
to the exciting possibility of new CP-odd phase(s) and flavor violating
parameters in B-decays. Primarily this seems to be the case in the time
dependent CP asymmetries in penguin dominated modes (e.g. B -> phi (eta') Ks).
We discuss these and other deviations from the SM and, as an illustration of
possible new physics scenarios, we examine the role of the Top Two Higgs
Doublet Model. This is a simple extension of the SM obtained by adding second
Higgs doublet in which the Yukawa interactions of the two Higgs doublets are
assigned in order to naturally account for the large top-quark mass.
Of course, many other extensions of the Standard Model could also account for
these experimental deviations. Clearly if one takes these deviations seriously
then some new particles in the 300 GeV to few TeV with associated new CP-odd
phase(s) are needed.Comment: 40 pages, 17 figures (png format), uses pdflate
Chiral behavior of the B(s,d)-Bbar(s,d) mixing amplitude in the Standard Model and beyond
We compute the chiral logarithmic corrections to the Bd and Bs mixing
amplitudes in the Standard Model and beyond. We then investigate the impact of
the inclusion of the lowest-lying scalar heavy-light states to the decay
constants and bag-parameters and show that this does not modify the pion chiral
logarithms, but it does produce corrections which are competitive in size with
the K- and eta-meson chiral logarithms. This conclusion is highly relevant to
the lattice studies since the pion chiral logarithms represent the most
important effect in guiding the chiral extrapolations of the lattice data for
these quantities. Also important is to stress that the pion chiral logarithmic
corrections are useful in guiding those extrapolations as long as Mpi << Delta,
where Delta is the mass gap between the scalar and pseudoscalar heavy-light
mesons.Comment: 16 pages, 5 figures (published version
Implications for the Constrained MSSM from a new prediction for b to s gamma
We re-examine the properties of the Constrained MSSM in light of updated
constraints, paying particular attention to the impact of the recent
substantial shift in the Standard Model prediction for BR(B to X_s gamma). With
the help of a Markov Chain Monte Carlo scanning technique, we vary all relevant
parameters simultaneously and derive Bayesian posterior probability maps. We
find that the case of \mu>0 remains favored, and that for \mu<0 it is
considerably more difficult to find a good global fit to current constraints.
In both cases we find a strong preference for a focus point region. This leads
to improved prospects for detecting neutralino dark matter in direct searches,
while superpartner searches at the LHC become more problematic, especially when
\mu<0. In contrast, prospects for exploring the whole mass range of the
lightest Higgs boson at the Tevatron and the LHC remain very good, which
should, along with dark matter searches, allow one to gain access to the
otherwise experimentally challenging focus point region. An alternative measure
of the mean quality-of-fit which we also employ implies that present data are
not yet constraining enough to draw more definite conclusions. We also comment
on the dependence of our results on the choice of priors and on some other
assumptions.Comment: JHEP versio
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