15 research outputs found
A consistent picture for large penguins in D -> pi+ pi-, K+ K-
A long-standing puzzle in charm physics is the large difference between the
D0 -> K+ K- and D0 -> pi+ pi- decay rates. Recently, the LHCb and CDF
collaborations reported a surprisingly large difference between the direct CP
asymmetries, Delta A_CP, in these two modes. We show that the two puzzles are
naturally related in the Standard Model via s- and d-quark "penguin
contractions". Their sum gives rise to Delta A_CP, while their difference
contributes to the two branching ratios with opposite sign. Assuming nominal
SU(3) breaking, a U-spin fit to the D0 -> K+ pi-, pi+ K-, pi+ pi-, K+ K- decay
rates yields large penguin contractions that naturally explain Delta A_CP.
Expectations for the individual CP asymmetries are also discussed.Comment: 24 pages, 8 figure
Physics of leptoquarks in precision experiments and at particle colliders
We present a comprehensive review of physics effects generated by leptoquarks
(LQs), i.e., hypothetical particles that can turn quarks into leptons and vice
versa, of either scalar or vector nature. These considerations include
discussion of possible completions of the Standard Model that contain LQ
fields. The main focus of the review is on those LQ scenarios that are not
problematic with regard to proton stability. We accordingly concentrate on the
phenomenology of light leptoquarks that is relevant for precision experiments
and particle colliders. Important constraints on LQ interactions with matter
are derived from precision low-energy observables such as electric dipole
moments, (g-2) of charged leptons, atomic parity violation, neutral meson
mixing, Kaon, B, and D meson decays, etc. We provide a general analysis of
indirect constraints on the strength of LQ interactions with the quarks and
leptons to make statements that are as model independent as possible. We
address complementary constraints that originate from electroweak precision
measurements, top, and Higgs physics. The Higgs physics analysis we present
covers not only the most recent but also expected results from the Large Hadron
Collider (LHC). We finally discuss direct LQ searches. Current experimental
situation is summarized and self-consistency of assumptions that go into
existing accelerator-based searches is discussed. A progress in making
next-to-leading order predictions for both pair and single LQ productions at
colliders is also outlined.Comment: 136 pages, 22 figures, typographical errors fixed, the Physics
Reports versio
Overview of the CKM Matrix
The current status of the determination of the elements of the
Cabibbo-Kobayashi-Maskawa quark-mixing matrix is reviewed. Tensions in the
global fits are highlighted. Particular attention is paid to progress in, and
prospects for, measurements of CP violation effects.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in
"Pramana - journal of physics", 17 pages, 13 figure
The Hunt for New Physics in the Flavour Sector with up vector-like quarks
We analyse the possible presence of New Physics (NP) in the Flavour Sector
and evaluate its potential for solving the tension between the experimental
values of \AJPKs and \BTNu with respect to the Standard Model (SM)
expectations. Updated model independent analyses, where NP contributions are
allowed in Bd - anti-Bd and Bs - anti-Bs transitions, suggest the need of New
Physics in the sector. A detailed analysis of recent Flavour data is then
presented in the framework of a simple extension of the SM, where a
vector-like isosinglet quark is added to the spectrum of the SM. Special
emphasis is given to the implications of this model for correlations among
various measurable quantities. We include constraints from all the relevant
quark flavour sectors and give precise predictions for selected rare processes.
We find important deviations from the SM in observables in the sector like
the semileptonic asymmetry \asld, and
. Other potential places where NP can show up include
, , , and
among others. The experimental data favours in this
model the existence of an up vector-like quark with a mass below
GeV at .Comment: 36 pages, 41 figures; minor changes and references added, matches
version accepted for publicatio
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe
Unified low-pressure compressor concept for engines of future high-speed micro-unmanned aerial vehicles
Twisted finite-volume corrections to K l3 decays with partially-quenched and rooted-staggered quarks
The high incidence of STR D21S1446 homozygosity in Han and She populations living in South Eastern China
Sensitivity to charged scalars in B -> D-(*)tau nu(tau) and B -> tau nu(tau) decays
We analyze the recent experimental evidence for an excess of tau-lepton production in several exclusive semileptonic B-meson decays in the context of two-Higgs-doublet models. These decay modes are sensitive to the exchange of charged scalars and constrain strongly their Yukawa interactions. While the usual Type-II scenario cannot accommodate the recent BaBar data, this is possible within more general models in which the charged-scalar couplings to up-type quarks are not as suppressed. Both the B -> D-(*)tau nu(tau) and the B -> tau nu(tau) data can be fitted within the framework of the Aligned Two-Higgs-Doublet Model, but the resulting parameter ranges are in conflict with the constraints from leptonic charm decays. This could indicate a departure from the family universality of the Yukawa couplings, beyond their characteristic fermion mass dependence. We discuss several new observables that are sensitive to a hypothetical charged-scalar contribution, demonstrating that they are well suited to distinguish between different scenarios of new physics in the scalar sector, and also between this group and models with different Dirac structures; their experimental study would therefore shed light on the relevance of scalar exchanges in semileptonic b -> c tau(-)(nu) over bar (tau) transitions