144 research outputs found
Chiral loop corrections to weak decays of B mesons to positive and negative parity charmed mesons
We determine chiral loop corrections to the B meson decay amplitudes to
positive and negative parity charmed mesons within a framework which combines
heavy quark and chiral symmetries. Then we investigate the impact of the
lowest-lying positive parity heavy mesons on the determination of the
Isgur-Wise functions. The corrections due to these states are competitive with
the contributions arising from K and eta meson loops. Since lattice studies
rely on the chiral behavior of the amplitudes we discuss the chiral limit of
our results. We find that the determination of the slope at zero recoil of the
Isgur-Wise function xi for the B transition to negative parity charm mesons is
moderately affected by the inclusion of new states, while the slope of
tau_{1/2} is affected significantly more.Comment: 10 pages, 4 figure
Implications of Flavor Dynamics for Fermion Triplet Leptogenesis
We analyze the importance of flavor effects in models in which leptogenesis
proceeds via the decay of Majorana electroweak triplets. We find that depending
on the relative strengths of gauge and Yukawa reactions the asymmetry can
be sizably enhanced, exceeding in some cases an order of magnitude level. We
also discuss the impact that such effects can have for TeV-scale triplets
showing that as long as the asymmetry is produced by the dynamics of the
lightest such triplet they are negligible, but open the possibility for
scenarios in which the asymmetry is generated above the TeV scale by heavier
states, possibly surviving the TeV triplet related washouts. We investigate
these cases and show how they can be disentangled at the LHC by using Majorana
triplet collider observables and, in the case of minimal type III see-saw
models even through lepton flavor violation observables.Comment: 22 pages, 9 figures, extended discussion on collider phenomenology,
references added. Version matches publication in JHE
Predictions from Heavy New Physics Interpretation of the Top Forward-Backward Asymmetry
We derive generic predictions at hadron colliders from the large
forward-backward asymmetry observed at the Tevatron, assuming the latter arises
from heavy new physics beyond the Standard Model. We use an effective field
theory approach to characterize the associated unknown dynamics. By fitting the
Tevatron t \bar t data we derive constraints on the form of the new physics.
Furthermore, we show that heavy new physics explaining the Tevatron data
generically enhances at high invariant masses both the top pair production
cross section and the charge asymmetry at the LHC. This enhancement can be
within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be
able to exclude a large class of models of heavy new physics or provide hints
for its presence. The same new physics implies a contribution to the
forward-backward asymmetry in bottom pair production at low invariant masses of
order a permil at most.Comment: 11 pages, 6 figures. v2: added remarks on EFT validity range, dijet
bounds and UV completions; matches published versio
Flavour physics from an approximate U(2)^3 symmetry
The quark sector of the Standard Model exhibits an approximate U(2)^3 flavour
symmetry. This symmetry, broken in specific directions dictated by minimality,
can explain the success of the Cabibbo-Kobayashi-Maskawa picture of flavour
mixing and CP violation, confirmed by the data so far, while allowing for
observable deviations from it, as expected in most models of ElectroWeak
Symmetry Breaking. Building on previous work in the specific context of
supersymmetry, we analyze the expected effects and we quantify the current
bounds in a general Effective Field Theory framework. As a further relevant
example we then show how the U(2)^3 symmetry and its breaking can be
implemented in a generic composite Higgs model and we make a first analysis of
its peculiar consequences. We also discuss how some partial extension of U(2)^3
to the lepton sector can arise, both in general and in composite Higgs models.
An optimistic though conceivable interpretation of the considerations developed
in this paper gives reasons to think that new physics searches in the flavour
sector may be about to explore an interesting realm of phenomena.Comment: 29 pages, 5 figure
Charming CP Violation and Dipole Operators from RS Flavor Anarchy
Recently the LHCb collaboration reported evidence for direct CP violation in
charm decays. The value is sufficiently large that either substantially
enhanced Standard Model contributions or non-Standard Model physics is required
to explain it. In the latter case only a limited number of possibilities would
be consistent with other existing flavor-changing constraints. We show that
warped extra dimensional models that explain the quark spectrum through flavor
anarchy can naturally give rise to contributions of the size required to
explain the the LHCb result. The D meson asymmetry arises through a sizable
CP-violating contribution to a chromomagnetic dipole operator. This happens
naturally without introducing inconsistencies with existing constraints in the
up quark sector. We discuss some subtleties in the loop calculation that are
similar to those in Higgs to \gamma\gamma. Loop-induced dipole operators in
warped scenarios and their composite analogs exhibit non-trivial dependence on
the Higgs profile, with the contributions monotonically decreasing when the
Higgs is pushed away from the IR brane. We show that the size of the dipole
operator quickly saturates as the Higgs profile approaches the IR brane,
implying small dependence on the precise details of the Higgs profile when it
is quasi IR localized. We also explain why the calculation of the coefficient
of the lowest dimension 5D operator is guaranteed to be finite. This is true
not only in the charm sector but also with other radiative processes such as
electric dipole moments, b to s\gamma, \epsilon'/\epsilon_K and \mu\ to
e\gamma. We furthermore discuss the interpretation of this contribution within
the framework of partial compositeness in four dimensions and highlight some
qualitative differences between the generic result of composite models and that
obtained for dynamics that reproduces the warped scenario.Comment: 14 page
Higgs After the Discovery: A Status Report
Recently, the ATLAS and CMS collaborations have announced the discovery of a
125 GeV particle, commensurable with the Higgs boson. We analyze the 2011 and
2012 LHC and Tevatron Higgs data in the context of simplified new physics
models, paying close attention to models which can enhance the diphoton rate
and allow for a natural weak-scale theory. Combining the available LHC and
Tevatron data in the ZZ* 4-lepton, WW* 2-lepton, diphoton, and b-bbar channels,
we derive constraints on the effective low-energy theory of the Higgs boson. We
map several simplified scenarios to the effective theory, capturing numerous
new physics models such as supersymmetry, composite Higgs, dilaton. We further
study models with extended Higgs sectors which can naturally enhance the
diphoton rate. We find that the current Higgs data are consistent with the
Standard Model Higgs boson and, consequently, the parameter space in all models
which go beyond the Standard Model is highly constrained.Comment: 37 pages; v2: ATLAS dijet-tag diphoton channel added, dilaton and
doublet-singlet bugs corrected, references added; v3: ATLAS WW channel
included, comments and references adde
Rare B decays and Tevatron top-pair asymmetry
The recent Tevatron result on the top quark forward-backward asymmetry, which
deviates from its standard model prediction by 3.4, has prompted many
authors to build new models to account for this anomaly. Among the various
proposals, we find that those mechanisms which produce via - or
-channel can have a strong correlation to the rare B decays. We demonstrate
this link by studying a model with a new charged gauge boson, . In terms of
the current measurements on decays, we conclude that the branching
ratio for is affected most by the new effects.
Furthermore, using the world average branching ratio for the exclusive B decays
at level, we discuss the allowed values for the new parameters.
Finally, we point out that the influence of the new physics effects on the
direct CP asymmetry in B decays is insignificant.Comment: 15 page, 6 figures, typos corrected and references added, final
version to appear journa
Proceedings of the 2nd Workshop on Flavor Symmetries and Consequences in Accelerators and Cosmology (FLASY12)
These are the proceedings of the 2nd Workshop on Flavor Symmetries and
Consequences in Accelerators and Cosmology, held 30 June 2012 - 4 July 2012,
Dortmund, Germany.Comment: Order 400 pages, several figures including the group picture v2:
corrected author list and contributio
Top quark forward-backward asymmetry in R-parity violating supersymmetry
The interaction of bottom squark-mediated top quark pair production,
occurring in the R-parity violating minimal supersymmetric standard model
(MSSM), is proposed as an explanation of the anomalously large
forward-backward asymmetry (FBA) observed at the Tevatron. We find that this
model can give a good fit to top quark data, both the inclusive and invariant
mass-dependent asymmetries, while remaining consistent (at the 2-
level) with the total and differential production cross-sections. The scenario
is challenged by strong constraints from atomic parity violation (APV), but we
point out an extra diagram for the effective down quark-Z vertex, involving the
same coupling constant as required for the FBA, which tends to weaken the APV
constraint, and which can nullify it for reasonable values of the top squark
masses and mixing angle. Large contributions to flavor-changing neutral
currents can be avoided if only the third generation of sparticles is light.Comment: 24 pages, 7 figures. v3: included LHC top production cross section
data; model still consistent at 2 sigma leve
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