arXiv subjects
Publications and source records attributed to O. Vives.
Supersymmetry exhibts new sources of CP violation. We discuss the implications of these new contributions to CP violation both in the K and B physics. We show that CP violation puts severe constraints on low energy SUSY, but it represents also a promising ground to look for signals of new physics.
In this work, we update the constraints on tree level FCNC couplings in the framework of a theory with n isosinglet vector-like down quarks. In this context, we emphasize the sensitivity of the B -> J/psi K_S CP asymmetry to the presence of new vector-like down quarks. This CP asymmetry, together with the rare decays B -> X_{s,d} l bar{l} and K -> pi nu bar{nu} are the best options to further constrain the FCNC tree level couplings or even to point out, in the near future, the possible presence of vector-like quarks in the low energy spectrum, as suggested by GUT theories or models of large extra dimensions at the TeV scale.
Tree-level Flavor-Changing Neutral Currents (FCNC) are characteristic of models with extra vector-like quarks. These new couplings can strongly modify the B^0 CP asymmetries without conflicting with low--energy constraints. In the light of a low CP asymmetry in B --> J/ψK_{S}, we discuss the implications of these contributions. We find that even these low values can be easily accommodated in these models. Furthermore, we show that the new data from B factories tend to favor an O(20) enhancement of the b --> d l \bar{l} transition over the SM expectation.
We study the implications on flavor changing neutral current and CP violating processes in the context of supersymmetric theories without a new flavor structure (flavor blind supersymmetry). The low energy parameters are determined by the running of the soft breaking terms from the grand unified scale with SUSY phases consistent with the EDM constraints. We find that the CP asymmetry in b --> s gamma can reach large values potentially measurable at B factories, especially in the low BR(b --> s gamma) region. We perform a fit of the unitarity triangle including all the relevant observables. In this case, no sizeable deviations from the SM expectations are found. Finally we analyze the SUSY contributions to the anomalous magnetic moment of the muon pointing out its impact on the b --> s gamma CP asymmetry and on the SUSY spectrum including chargino and stop masses.
CP violation plays a privileged role in our quest for new physics beyond the electroweak standard model (SM). In the SM the violation of CP in the weak interactions has a single source: the phase of the quark mixing matrix (the CKM matrix, for Cabibbo-Kobayashi-Maskawa). Most extensions of the SM exhibit new sources of CP violation. For instance, the truly minimal supersymmetric extension of the SM (CMSSM) has two new phases in addition to the CKM phase. Given that CP violation is so tiny in the kaon system, is still largely unexplored in B physics and is negligibly small in the electric dipole moments, it is clear that new physics may have a good chance to manifest some departure from the SM in this particularly challenging class of rare phenomena. On the other hand, it is also apparent that CP violation generally represents a major constraint on any attempt at model building beyond the SM. In this review we tackle these two sides of the relation between CP violation and new physics. Our focus will be on the potentialities to use CP violation as a probe on Supersymmetric (SUSY) extensions of the SM. We wish to clarify the extent to which such indirect signals for SUSY are linked to a fundamental theoretical issue: is there a relation between the mechanism that originates the whole flavor structure and the mechanism that is responsible for the breaking of supersymmetry? Different ways to answer this question lead to quite different expectations for CP violation in B physics.
We show that general Minimal Supersymmetric extensions of the Standard Model (MSSM) allow for a CP asymmetry in B --> J/psi K(S) well bellow the SM expectations with dominant Supersymmetric contributions to epsilon_K and epsilon'/epsilon. Indeed, we provide an explicit example of an MSSM with non-universal soft breaking terms fully consistent with the low results of this asymmetry recently announced by Babar and Belle collaborations.
We analyze the flavor structure of the trilinear couplings in the different theoretical models of SUSY breaking. We generically obtain A_{ij}= A^L_i + A^R_j in all the models examined. In fact, this is the rigorous form when SUSY breaking effects appear through the Kahler metric of chiral fields or through wave-function renormalization. Indeed, the low-energy phenomenological requirements from the absence of charge and color breaking minima and the measurements in flavor changing neutral current (FCNC) observables strongly favor this restricted form of the trilinear matrices. As a straightforward consequence, the number of unknown parameters associated with the trilinear couplings is decreased in a factor of 2.
We analyze CP violation and Flavor Changing effects in a general Minimal Supersymmetric extension of the Standard Model with arbitrary non-universal soft-breaking terms. We show that, in this conditions, large FCNC effects are naturally expected in the Kaon system, even in the absence of quark-squark flavor misalignment. On the other hand, the B system is only sensitive to new supersymmetric contributions if the non-universality implies, not only different soft term for the three generations but also the presence of a quark-squark misalignment much larger that the corresponding CKM mixing. The only exception to this rule are processes where the chirality changing contributions proportional to tan beta are leading (for instance b -> s gamma).
We address the question of the relation between supersymmetry breaking and the origin of flavor in the context of CP violating phenomena. We prove that, in the absence of the Cabibbo-Kobayashi-Maskawa phase, a general Minimal Supersymmetric Standard Model with all possible phases in the soft-breaking terms, but no new flavor structure beyond the usual Yukawa matrices, can never give a sizeable contribution to $ε_K$, $ε^\prime/ε$ or hadronic $B^0$ CP asymmetries. Observation of supersymmetric contributions to CP asymmetries in B decays would hint at a non-flavor blind mechanism of supersymmetry breaking.
In this talk, we address the possibility of finding supersymmetry through indirect searches in the K and B systems. We prove that, in the absence of the Cabibbo-Kobayashi-Maskawa phase, a general Minimal Supersymmetric Standard Model with all possible phases in the soft-breaking terms, but no new flavor structure beyond the usual Yukawa matrices, can never give a sizeable contribution to $ε_K$, $ε^\prime/ε$ or hadronic B^0 CP asymmetries. However, Minimal Supersymmetric models with additional flavor structures in the soft-supersymmetry breaking terms can produce large deviations from the Standard Model predictions. Hence, observation of supersymmetric contributions to CP asymmetries in B decays would be the first sign of the existence of new flavor structures in the soft-terms and would hint at a non-flavor blind mechanism of supersymmetry breaking.
We address the following question. Take the Constrained Minimal Supersymmetric Standard Model (CMSSM) with the two CP violating SUSY phases different from zero, and neglect the bound coming from the electric dipole moment of the neutron (EDM): is it possible to fully account for CP violation in the kaon and B systems using only the SUSY contributions with vanishing CKM phase? We show that the ${BR}(B\to X_{s} γ)$ constraint, though CP conserving, forces a negative answer to the above question. This implies that, even in the regions of the CMSSM where a cancellation of different contributions to the EDM allows for large SUSY phases, it is not possible to exploit the SUSY phases to fully account for observable CP violation. Hence to have sizeable SUSY contributions to CP violation, one needs new flavor structures in the sfermion mass matrices beyond the usual CKM matrix.
In this work, we study possible new contributions to $ε_{K}$ and $ε_{B}$ in the MSSM with large supersymmetric phases. We show that, in the CMSSM, the constrains coming from the experimental measure of the $b \to s γ$ decay imply that these contributions are too small to be detected in CP violation experiments with the available sensitivity.
We analyze CP violation in supersymmetric extensions of the Standard Model with heavy scalar fermions of the first two generations. Neglecting intergenerational mixing in the sfemion mass matrices and thus considering only chargino, charged Higgs and W--boson diagrams we show that it is possible to fully account for CP violation in the kaon system even in the absence of the standard CKM phase. This opens new possibilities for large supersymmetric contributions to CP violation in the B system.
We study the $γ$-Z interference in the process $e^+ e^-\to Υ\to τ^+ τ^-$ as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and background diagrams and the spin density matrix of the final state is discussed. The spin analyzer of the $τ$'s is illustrated with the decays $πν$ and $ρν\to (ππ) ν$. With $10^8 Υ$ a sensitivity to $g_V^b$ of a few per cent could be reachable.
We show that the study of CP asymmetries in neutral B-meson decays provides a very sensitive probe of flavour-changing neutral currents (FCNC). We introduce two new angles, $α_{SM}$ and $β_{SM}$, whose main feature is that they can be readily obtained from the measurement of the CP asymmetries $a_{J/ψK_s}$, $a_{π^+ π^-}$ and the ratio $R_u \equiv|V_{ud}V_{ub}^*|/|V_{cd}V_{cb}^*|$, providing a quantitative test of the presence of new physics in a model-independent way. Assuming that new physics is due to the presence of an isosinglet down-type quark, we indicate how to reconstruct the unitarity quadrangles and point out that the measurements of the above asymmetries, within the expected experimental errors, may detect FCNC effects, even for values of $|\sum_{i=1}^3 V_{id} V_{ib}^* / (V_{td} V_{tb}^*)| $ at the level of a few times $10^{-2}$.
We explore the sensitivity to a non vanishing neutrino mass offered by dynamical observables, i.e., branching ratios and polarizations. The longitudinal polarization in the C.M. frame decreases by a 4% for $D^+ \rightarrow τ^+ ν_τ$ and $m_{ν_τ}=24$ MeV. Taking advantage of the fact that the polarization is a Lorentz variant quantity, we study the polarization effects in a boosted frame. By means of a neutrino beam, produced by a high velocity boosted parent able to flip the neutrino helicity, we find that an enhanced left-handed neutrino deficit, induced by a Wigner rotation, appears.
We analyze the possibilities that the proposed $Φ$-factories offer to measure $γ-Z$ interference. In the unpolarized beam case, we study different signatures in the $ρπ$ channel, taking advantage of the presence of the near-by $a_1$ resonance. We build a C-odd forward-backward asymmetry, estimated to be around $10^{-5}$, and (P-even, T-even) and (P-odd, T-odd) alignments of the $ρ$, to be seen from the angular distribution of its $ππ$ decay products. With polarized electrons a left-right asymmetry around $2\times 10^{-4}$ is present in all channels. At leading order this asymmetry is independent of hadronic matrix elements and is sensitive to the $Z^0-s\bar{s}$ vector coupling. In the $ρπ$ channel, a combined left-right forward-backward asymmetry is considered.