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Christopher Smith

Publications and source records attributed to Christopher Smith.

At least 55 records · Page 3Linked to original sources
arXiv2011

The s ---> d gamma decay in and beyond the Standard Model

The New Physics sensitivity of the s ---> d gamma transition and its accessibility through hadronic processes are thoroughly investigated. Firstly, the Standard Model predictions for the direct CP-violating observables in radiative K decays are systematically improved. Besides, the magnetic contribution to epsilon prime is estimated and found subleading, even in the presence of New Physics, and a new strategy to resolve its electroweak versus QCD penguin fraction is identified. Secondly, the signatures of a series of New Physics scenarios, characterized as model-independently as possible in terms of their underlying dynamics, are investigated by combining the information from all the FCNC transitions in the s ---> d sector.

hep-ph↗
arXiv2010

Rare K and B decays with non-standard missing energy

The rare K and B semileptonic decays into neutrino pairs are well-known to be extremely sensitive to non-standard physics in the quark sector. In this talk, their capabilities to signal New Physics in the leptonic sector, or even to reveal entirely new invisible sectors, are analyzed.

hep-ph↗
arXiv2010

Theoretical perspective on the NA62 physics program

Soon the NA62 experiment will start looking for the rare K+ ---> pi+ nu nu bar decay. In this talk, its theoretical interests, together with those of the neutral rare decays KL ---> pi0 nu nu bar, KL ---> pi0 e+ e-, and KL ---> pi0 mu+ mu-, are briefly reviewed. Then, other possible targets for NA62 are discussed, among which the dominant semileptonic decays, the radiative decays, as well as the lepton-flavor violating decays.

hep-ph↗
arXiv2009

The matrix type of purely infinite simple Leavitt path algebras

Let $R$ denote the purely infinite simple unital Leavitt path algebra $L(E)$. We completely determine the pairs of positive integers $(c,d)$ for which there is an isomorphism of matrix rings $M_c(R)\cong M_d(R)$, in terms of the order of $[1_R]$ in the Grothendieck group $K_0(R)$.

math.RA↗
arXiv2009

Minimal flavor violation in supersymmetric theories

The minimal flavor violation hypothesis is presented in the context of the MSSM. Its fundamental principles are introduced and motivated, and its phenomenological consequences for FCNC and CP-violating observables as well as for R-parity violating processes are briefly described.

hep-ph↗
arXiv2009

Long-distance effects in rare and radiative K decays

The electroweak structures of the FCNC-induced rare and radiative K decays are presented. While the former decays are sensitive to short-distance physics and offer exceptional probes for new physics, the latter are dominated by long-distance physics. Even so, they should not be set aside since they constitute essential ingredients to control the hadronic uncertainties occurring for the rare decays. This is illustrated by systematically reviewing the phenomenological strategies currently in use to cleanly predict the rare K decay rates in the Standard Model.

hep-ph↗
arXiv2009

Tree-level contributions to the rare decays B+ --> pi+ nu anti-nu, B+ --> K+ nu anti-nu, and B+ --> K*+ nu anti-nu in the Standard Model

The tree-level contributions to the rare decays B+ --> pi+ nu anti-nu, B+ --> K+ nu anti-nu, and B+ --> K*+ nu anti-nu are analyzed and compared to those occurring in K+ --> pi+ nu anti-nu, D+ --> pi+ nu anti-nu, and Ds+ --> pi+ nu anti-nu. It is shown that these purely long-distance contributions, arising from the exchange of a charged lepton, can be significant in B+ decays for an intermediate tau, potentially blurring the distinction between the modes used to extract B --> tau nu and those used to probe the genuine short-distance b --> (s,d) nu anti-nu FCNC transitions. Numerically, the tree-level contributions are found to account for 97%, 12% and 14% of the total B+ --> pi+ nu anti-nu, B+ --> K+ nu anti-nu, and B+ --> K*+ nu anti-nu rates, respectively.

hep-ph↗
arXiv2009

EDM constraints on flavored CP-violating phases

The CP-violating phenomenology of the MSSM with Minimal Flavor Violation (MFV) in the lepton sector is revisited. To this end, the most general parametrizations of the slepton soft-breaking terms are constructed assuming a seesaw mechanism of type I. After a critical reassessment of how the CP-symmetry is broken within the MFV framework, all possible CP-violating phases are introduced. From the strong hierarchy of their contributions to the Electric Dipole Moments (EDMs), these phases are split into three classes: flavor-blind, flavor-diagonal and flavor off-diagonal. In particular, the phases from the neutrino sector belong to the last class; they start to contribute only at the second order in the mass-insertion approximation and have thus a negligible effect. It is then shown that to each class of phases corresponds a unique largely dominant term in the MFV expansion. Numerically, for a realistic range of MSSM and neutrino parameters, such that B(mu --> e gamma) does not exceed its experimental bound, the three types of phases are found to be allowed by the current bound on the electron EDM, though the next generation of experiments should constrain tightly the flavor-blind phase. Finally, we relax the MFV hypothesis and show how in the general MSSM, the MFV operator basis can be used to judge of the naturality of the slepton soft-breaking terms.

hep-ph↗
arXiv2009

Supersymmetric models with minimal flavour violation and their running

We revisit the formulation of the principle of minimal flavor violation (MFV) in the minimal supersymmetric extension of the standard model, both at moderate and large tan(beta), and with or without new CP-violating phases. We introduce a counting rule which keeps track of the highly hierarchical structure of the Yukawa matrices. In this manner, we are able to control systematically which terms can be discarded in the soft SUSY breaking part of the Lagrangian. We argue that for the implementation of this counting rule, it is convenient to introduce a new basis of matrices in which both the squark (and slepton) mass terms as well as the trilinear couplings can be expanded. We derive the RGE for the MFV parameters and show that the beta functions also respect the counting rule. For moderate tan(beta), we provide explicit analytic solutions of these RGE and illustrate their behaviour by analyzing the neighbourhood (also switching on new phases) of the SPS-1a benchmark point. We then show that even in the case of large tan(beta), the RGE remain valid and that the analytic solutions obtained for moderate tan(beta) still allow us to understand the most important features of the running of the parameters, as illustrated with the help of the SPS-4 benchmark point.

hep-ph↗
arXiv2008

Minimal Flavor Violation as an alternative to R-parity

A peculiar aspect of the MSSM, the simplest supersymmetric extension of the Standard Model, is that it is usually defined including an ad hoc symmetry, R-parity, whose sole purpose is to forbid rapid proton decay. This symmetry deeply alters the phenomenology of the MSSM, and renders the experimental search strategies quite involved. Besides, the MSSM suffers from a number of flavor puzzles. Generically, the superparticle contributions to Flavor Changing Neutral Currents (FCNC) are too large compared to experiment, both in the quark and lepton sectors. The Minimal Flavor Violation (MFV) hypothesis aims at suppressing these contributions, and when enforced as a symmetry principle, achieves this in a very natural and systematic way. In this talk, it will be shown that imposing MFV is not only able to suppress supersymmetric contributions to FCNC, it also naturally explains the apparent stability of the proton. As a result, R-parity can be avoided altogether, motivating the search for supersymmetry through simpler channels, like for example single stop resonant production, whose strength is predicted by MFV.

hep-ph↗
arXiv2008

Minimal Flavor Violation, Seesaw, and R-parity

The Minimal Flavor Violation hypothesis (MFV) is extended to the R-parity violating MSSM, supplemented with a simple seesaw mechanism. The requirement of MFV is shown to suppress lepton and baryon-number violating couplings sufficiently to pass all experimental bounds, in particular those for proton decay, and is thus a viable alternative to R-parity. The phenomenological consequences for FCNC, LFV and colliders are briefly discussed. Typically, MFV predicts sizeable baryon-number violation in some characteristic channels, like single stop resonant production.

hep-ph↗
arXiv2007

What rare K decays can tell about the MSSM

The supersymmetric contributions to the theoretically clean K+ --> pi+ nu nu bar, KL --> pi0 nu nu bar, KL --> pi0 e+ e- and KL --> pi0 mu+ mu- decays are briefly reviewed. Particular emphasis is laid on the information one could get on the MSSM flavor sector from a combined study of the four modes.

hep-ph↗
arXiv2007

Improved estimates of rare K decay matrix-elements from Kl3 decays

The estimation of rare K decay matrix-elements from Kl3 experimental data is extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative corrections are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form-factors, for which the theoretical control is excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL --> pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct CP-violating contribution to KL --> pi0 l+ l-. They could be reduced even further with better experimental data for the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric errors for B(K --> pi nu nubar) and for the direct CP-violating contributions to B(KL --> pi0 l+ l-) are now completely dominated by those on the short-distance physics.

hep-ph↗
arXiv2007

Recent progress on supersymmetric effects in rare K decays

The dominant MSSM effects in the rare K decays, K+ --> pi+ nu nu bar, KL --> pi0 nu nu bar, KL --> pi0 e+ e- and KL --> pi0 mu+ mu-, are discussed both within and without the minimal flavor violation hypothesis, at moderate and large tangent beta. In each case, the sensitivities to MSSM soft-breaking terms are compared, laying emphasis on possible correlations among observables. In most scenarios, rare K decays offer unique windows into the Delta S=1 sector of the soft-breaking terms. Therefore, together with B-physics and collider observables, these modes will be essential for reconstructing the still elusive SUSY-breaking mechanism.

hep-ph↗
arXiv2007

Rare K decays in the Standard Model

The very clean theoretical predictions for the rare decays K --> pi nu nu_bar and KL --> pi0 l+ l- are reviewed, and their various theoretical inputs summarized. The less favorable situation for KL --> mu+ mu- is also commented.

hep-ph↗
arXiv2006

KL to pi0 e+ e- and KL to pi0 mu+ mu- : A binary star on the stage of flavor physics

A systematic analysis of New Physics impacts on the rare decays KL to pi0 l+ l- is performed. Thanks to their different sensitivities to flavor-changing local effective interactions, these two modes could provide valuable information on the nature of the possible New Physics at play. In particular, a combined measurement of both modes could disentangle scalar/pseudoscalar from vector or axial-vector contributions. For the latter, model-independent bounds are derived. Finally, the KL to pi0 mu+ mu- forward-backward CP-asymmetry is considered, and shown to give interesting complementary information.

hep-ph↗
arXiv2006

Tracking down penguins at the poles

QCD penguins are responsible for about 2/3 of the Delta I=1/2 rule in K to pi pi decays, as inferred from a combined analysis of K to pi pi and KL to gamma gamma. Further tests based on the decays KS to pi0 gamma gamma and K+ to pi+ gamma gamma are proposed. New insights into the treatment of pi0, eta, eta' pole amplitudes are also reported.

hep-ph↗