19 research outputs found
Lessons from Recent Measurements of D-\bar D Mixing
An impressive progress in measurements of the D-\bar D mixing parameters has
been made in recent years. We explore the implications of these measurements to
models of new physics, especially in view of recent upper bounds on the amount
of CP violation. We update the constraints on non-renormalizable four-quark
operators. We show that the experiments are close to probing minimally flavor
violating models with large tan beta. The data challenge models with a scale of
order TeV where the flavor violation in the down sector is suppressed by
alignment and, in particular, certain classes of supersymmetric models and of
warped extra dimension models.Comment: 20 pages, 1 figure. Added references, minor corrections and
clarifications. Matches published versio
Top B Physics at the LHC
In top-pair events where at least one of the tops decays semi-leptonically,
the identification of the lepton charge allows to tag not only the top charge
but also that of the subsequent b quark. In cases where the b also decays
semi-leptonically, the charge of the two leptons can be used to probe CP
violation in heavy flavor mixing and decays. This strategy to measure CP
violation is independent of those adopted so far in experiments, and can
already constrain non Standard Model sources of CP violation with current and
near future LHC data. To demonstrate the potential of this method we construct
two CP asymmetries based on same-sign and opposite-sign leptons and estimate
their sensitivities. This proposal opens a new window for doing precision
measurements of CP violation in b and c quark physics via high p_T processes at
ATLAS and CMS.Comment: 5 pages, 2 figures. v2: Slightly improved the b-charge association
analysis; some discussions and clarifications added; fixed typos in Eqs.
(29)-(32). Matches published versio
Implications of the Measurement of Ultra-Massive Boosted Jets at CDF
The CDF collaboration recently reported an upper limit on boosted top pair
production and noted a significant excess above the estimated background of
events with two ultra-massive boosted jets. We discuss the interpretation of
the measurement and its fundamental implications. In case new physics is
involved, the most naive contribution is from a new particle produced with a
cross section that is a few times higher than that of the top quark and a
sizable hadronic branching ratio. We quantify the resulting tension of a
possible larger top pair cross section with the absence of excess found in
events with one massive boosted jet and missing energy. The measured planar
flow distribution shows deviation from CDF's Pythia QCD prediction at high
planarity, while we find a somewhat smaller deviation when comparing with other
Monte Carlo tools. As a simple toy model, we analyze the case of a light gluino
with R-parity violation and show that it can be made consistent with the data.Comment: 5 pages, 2 figures and 2 tables. v2: Added a Monte Carlo estimation
of the QCD background and some other minor correction. v3: Some
clarifications and modifications (including in Fig. 2), added references;
matches published versio
Extraordinary Phenomenology from Warped Flavor Triviality
Anarchic warped extra dimensional models provide a solution to the hierarchy
problem. They can also account for the observed flavor hierarchies, but only at
the expense of little hierarchy and CP problems, which naturally require a
Kaluza-Klein (KK) scale beyond the LHC reach. We have recently shown that when
flavor issues are decoupled, and assumed to be solved by UV physics, the
framework's parameter space greatly opens. Given the possibility of a lower KK
scale and composite light quarks, this class of flavor triviality models enjoys
a rather exceptional phenomenology, which is the focus of this letter. We also
revisit the anarchic RS EDM problem, which requires m_{KK} > 8 TeV, and show
that it is solved within flavor triviality models. Interestingly, our framework
can induce a sizable differential t \bar{t} forward-backward asymmetry, and
leads to an excess of massive boosted di-jet events, which may be linked to the
recent findings of the CDF collaboration. This feature may be observed by
looking at the corresponding planar flow distribution, which is presented here.
Finally we point out that the celebrated standard model preference towards a
light Higgs is significantly reduced within our framework.Comment: 6 pages, 3 figures. Updated the EDM bound on the anarchic scenario;
extended discussion on the KK gluon's width, discovery potential and
resulting dijet signal; matches published versio
On the Universality of CP Violation in Delta F = 1 Processes
We show that new physics which breaks the left-handed SU(3)_Q quark flavor
symmetry induces contributions to CP violation in Delta F = 1 couplings which
are approximately universal, in that they are not affected by flavor rotations
between the up and the down mass bases. (Only the short distance contributions
are universal, while observables are also affected by hadronic matrix
elements.) Therefore, such flavor violation cannot be aligned, and is
constrained by the strongest bound from either the up or the down sectors. We
use this result to show that the bound from eps'/eps prohibits an SU(3)_Q
breaking explanation of the recent LHCb evidence for CP violation in D meson
decays. Another consequence of this universality is that supersymmetric
alignment models with a moderate mediation scale are consistent with the data,
and are harder to probe via CP violating observables. With current constraints,
therefore, squarks need not be degenerate. However, future improvements in the
measurement of CP violation in D-Dbar mixing will start to probe alignment
models.Comment: 10 pages, 2 figures. Clarifications and references adde