Lepton flavor violation in minimal flavor violation extensions of the seesaw

A minimal flavour violation hypothesis for leptons can be implemented essentially in two ways that are compatible with a type-I seesaw structure with three heavy singlet neutrinos $N$, and that satisfy the requirement of being predictive, in the sense that all lepton flavor violating (LFV) effects can be expressed in terms of low energy observables. The first realization is CP conserving and is based on the flavor group $SU(3)_e\times SU(3)_\ell\times O(3)_N$ (being $e$ and $\ell$ the SU(2) singlet and doublet leptons). The second realization allows for CP violation and is based on $SU(3)_e\times SU(3)_{\ell+N}$. I review the main features of the two schemes and point out their different implications for LFV observables.Comment: 5 pages. Invited talk at the Workshop on e+ e- Collisions from \Phi\ to \Psi\ (PHIPSI08)}, September 19-22, 2011, Novosibirsk, Russi

CPV tests with rare kaon decays

The K_S \to pi+/- e+ e- decay mode has been investigated using the data collected in 2002 by the NA48/1 collaboration. With about 23k signal events and 59k K_L \to pi+ pi- pi0_D normalization decays, the K_S \to pi+ pi- e+ e- branching ratio was determined. This result is also used to set an upper limit on the presence of E1 direct emission in the decay amplitude. The CP-violating asymmetry has been also measured. We report on measurements of the rare decays K +/- \to pi+/- e+ e- and K+/- \to pi+/- mu+ mu- . The full NA48/2 data set was analyzed, leading to more than 7200 reconstructed events in the electronic and more than 3000 events in the muonic channel, the latter exceeding the total existing statistics by a factor of four. For both channels the selected events are almost background-free. From these events, we have determined the branching fraction and form factors of K+/- \to pi+/- e+ e- using different theoretical models. Our results improve the existing world averages significantly. In addition, we measured the CP violating asymmetry between K+ and K- in this channel to be less than a few percent.Comment: 4 pages, 1 figure, To appear in the proceedings of IX International Conference on Hyperons, Charm and Beauty Hadrons (BEACH2010), Perugia, Italy, 21-26 June 201

The Other Natural Two Higgs Doublet Model

We characterize models where electroweak symmetry breaking is driven by two light Higgs doublets arising as pseudo-Nambu-Goldstone bosons of new dynamics above the weak scale. They represent the simplest natural two Higgs doublet alternative to supersymmetry. We construct their low-energy effective Lagrangian making only few specific assumptions about the strong sector. These concern their global symmetries, their patterns of spontaneous breaking and the sources of explicit breaking. In particular we assume that all the explicit breaking is associated with the couplings of the strong sector to the Standard Model fields, that is gauge and (proto)-Yukawa interactions. Under those assumptions the scalar potential is determined at lowest order by very few free parameters associated to the top sector. Another crucial property of our scenarios is the presence of a discrete symmetry, in addition to custodial SO(4), that controls the $T$-parameter. That can either be simple CP or a $Z_2$ that distinguishes the two Higgs doublets. Among various possibilities we study in detail models based on SO(6)/SO(4)$\times$ SO(2), focussing on their predictions for the structure of the scalar spectrum and the deviations of their couplings from those of a generic renormalizable two Higgs doublet model.Comment: 54 page

Direct test of time-reversal symmetry in the entangled neutral kaon system at a ϕ\phi-factory

We present a novel method to perform a direct T (time reversal) symmetry test in the neutral kaon system, independent of any CP and/or CPT symmetry tests. This is based on the comparison of suitable transition probabilities, where the required interchange of in out states for a given process is obtained exploiting the Einstein-Podolsky-Rosen correlations of neutral kaon pairs produced at a $\phi$-factory. In the time distribution between the two decays, we compare a reference transition like the one defined by the time ordered decays $(\ell^-,\pi\pi)$ with the T -conjugated one defined by $(3\pi^0, \ell^+)$. With the use of this and other T conjugated comparisons, the KLOE-2 experiment at DA$\Phi$NE could make a significant test

Color-Octet-Electroweak-Doublet Scalars and the CDF Dijet Anomaly

We study the phenomenology of color-octet scalars in the (8, 2)1/2 representation in the context of the 3.2\sigma excess, in the dijet invariant mass spectrum of the W+jj final state, recently observed by the CDF collaboration. We consider the region of parameter space with a sizable mass splitting between the charged and neutral color-octet scalars and consistent with electroweak precision data. We implement the principle of Minimal Flavor Violation (MFV) in order to suppress FCNC currents and reduce the number of free parameters. The excess in the W+jj channel corresponds to the charged current decay of the heavier neutral octet scalar into its lighter charged partner which decays into the two jets. In the MFV scenario, the production of the neutral color-octet is dominated by gluon fusion due to the Yukawa suppression of production via initial state quarks. As a result, no visible excess is expected in the \gamma+jj channel due to Yukawa and CKM suppression. Contributions to the Z+jj final state are suppressed for a mass spectrum where the decay of the heavier color-octet to this final state is mediated by an off-shell neutral color-octet partner. MFV allows one to control fraction of bottom quarks in the final state jets by a single ratio of two free parameters.Comment: 14 pages, 6 figures, typos corrected, references added, text and figures modified in some places for better clarity, version to appear in Physics Letters

Effective Theory of Resonant Leptogenesis in the Closed-Time-Path Approach

We describe mixing scalar particles and Majorana fermions using Closed-Time-Path methods. From the Kadanoff-Baym equations, we obtain the charge asymmetry, that is generated from decays and inverse decays of the mixing particles. Within one single formalism, we thereby treat Leptogenesis from oscillations and recover as well the standard results for the asymmetry in Resonant Leptogenesis, which apply when the oscillation frequency is much larger than the decay rate. Analytic solutions for two mixing neutral particles in a constant-temperature background illustrate our results qualitatively. We also perform the modification of the kinetic equations that is necessary in order to take account of the expansion of the Universe and the washout of the asymmetry.Comment: 46 pages, typos corrected, clarifying details adde

Complete next-to-leading order gluino contributions to b--> s gamma and b--> s g

We present the first complete order alpha_s corrections to the Wilson coefficients (at the high scale) of the various versions of magnetic and chromomagnetic operators which are induced by a squark-gluino exchange. For this matching calculation, we work out the on-shell amplitudes b--> s gamma and b --> s g, both in the full and in the effective theory up to order alpha_s^2. The most difficult part of the calculation is the evaluation of the two-loop diagrams in the full theory; these can be split into two classes: a) diagrams with one gluino and a virtual gluon; b) diagrams with two gluinos or with one gluino and a four-squark vertex. Accordingly, the Wilson coefficients can be split into a part a) and a part b). While part b) of the Wilson coefficients is presented in this paper for the first time, part a) was given in (Bobeth et al.). We checked their results for the coefficients of the magnetic operators and found perfect agreement. Moreover, we work out the renormalization procedure in great detail. Our results for the complete next-to-leading order Wilson coefficients are fully analytic, but far too long to be printed. We therefore publish them in the form of a C++ program. They constitute a crucial building block for the phenomenological next-to-leading logarithmic analysis of the branching ratio Bbar --> X_s gamma in a supersymmetric model beyond minimal flavor violation.Comment: 38 pages, including c++ cod

Invariants and flavour in the general Two Higgs Doublet Model

The flavour structure of the general Two Higgs Doublet Model (2HDM) is analysed and a detailed study of the parameter space is presented, showing that flavour mixing in the 2HDM can be parametrized by various unitary matrices which arise from the misalignment in flavour space between pairs of various Hermitian flavour matrices which can be constructed within the model. This is entirely analogous to the generation of the CKM matrix in the Standard Model (SM). We construct weak basis invariants which can give insight into the physical implications of any flavour model, written in an arbitrary weak basis (WB) in the context of 2HDM. We apply this technique to two special cases, models with MFV and models with NNI structures. In both cases non-trivial CP-odd WB invariants arise in a mass power order much smaller than what one encounters in the SM, which can have important implications for baryogenesis in the framework of the general 2HDM

Absolute luminosity measurements with the LHCb detector at the LHC

Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic "van der Meer scan" method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overall precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.Comment: 48 pages, 19 figures. Results unchanged, improved clarity of Table 6, 9 and 10 and corresponding explanation in the tex

Absolute luminosity measurements with the LHCb detector at the LHC

Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic "van der Meer scan" method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overall precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.Comment: 48 pages, 19 figures. Results unchanged, improved clarity of Table 6, 9 and 10 and corresponding explanation in the tex