arXiv subjects

Paride Paradisi

Publications and source records attributed to Paride Paradisi.

54 records · Page 3Linked to original sources

arXiv2012

Direct CP violation in charm and flavor mixing beyond the SM

We analyze possible interpretations of the recent LHCb evidence for CP violation in D meson decays in terms of physics beyond the Standard Model. On general grounds, models in which the primary source of flavor violation is linked to the breaking of chiral symmetry (left-right flavor mixing) are natural candidates to explain this effect, via enhanced chromomagnetic operators. In the case of supersymmetric models, we identify two motivated scenarios: disoriented A-terms and split families. These structures predict other non-standard signals, such as nuclear EDMs close to their present bounds and, possibly, tiny but visible deviations in K and B physics, or even sizable flavor-violating processes involving the top quark or the stops. Some of these connections, especially the one with nuclear EDMs, hold beyond supersymmetry, as illustrated with the help of prototype non-supersymmetric models.

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arXiv2010

Non-Standard Neutrino Interactions at One Loop

Neutrino oscillation experiments are known to be sensitive to Non-Standard Interactions (NSIs). We extend the NSI formalism to include one-loop effects. We discuss universal effects induced by corrections to the tree level W exchange, as well as non-universal effects that can arise from scalar charged current interactions. We show how the parameters that can be extracted from the experiments are obtained from various loop amplitudes, which include vertex corrections, wave function renormalizations, mass corrections as well as box diagrams. As an illustrative example, we discuss NSIs at one loop in the Minimal Supersymmetric Standard Model (MSSM) with generic lepton flavor violating sources in the soft sector. We argue that the size of one-loop NSIs can be large enough to be probed in future neutrino oscillation experiments.

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arXiv2010

Footprints of SUSY GUTs in Flavour Physics

Supersymmetric (SUSY) Grand Unified theories (GUTs) generally predict FCNC and CP violating processes to occur both in the leptonic and hadronic sectors. Assuming an underlying SU(5) group plus right-handed neutrinos (RN), we perform an extensive study of FCNC and CP violation, analyzing the correlations between leptonic and hadronic processes like mu-> e gamma and K-Kbar mixing, tau->mu gamma and b -> s transitions such as B_d -> phi K_s and Bs-Bsbar mixing. Moreover, we examine the impact of the considered scenario on the UT analyses, monitoring the low energy consequences implied by possible solutions to the various tensions in the present UT analyses. We compare the phenomenological implications of this NP scenario with the ones of supersymmetric flavour models finding a few striking differences that could allow to distinguish these different NP models.

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arXiv2010

EDMs vs. CPV in B_{s,d} mixing in two Higgs doublet models with MFV

We analyze the correlations between electric dipole moments (EDMs) of the neutron and heavy atoms and CP violation in B_{s,d} mixing in two Higgs doublet models respecting the Minimal Flavour Violation hypothesis, with flavour-blind CP-violating (CPV) phases. In particular, we consider the case of flavour-blind CPV phases from i) the Yukawa interactions and ii) the Higgs potential. We show that in both cases the upper bounds on the above EDMs do not forbid sizable non-standard CPV effects in B_s mixing. However, if a large CPV phase in B_s mixing will be confirmed, this will imply EDMs very close to their present experimental bounds, within the reach of the next generation of experiments, as well as BR(B_{s,d}-> mu^+ mu^-) typically largely enhanced over its SM expectation. The two flavour-blind CPV mechanisms can be distinguished through the correlation between S_psi K_S and S_psi phi that is strikingly different if only one of them is relevant. Which of these two CPV mechanisms dominates depends on the precise values of S_psi phi and S_psi K_S, as well as on the CKM phase (as determined by tree-level processes). Current data seems to show a mild preference for a hybrid scenario where both these mechanisms are at work.

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arXiv2010

The electron and neutron EDM from supersymmetric see-saw thresholds

We consider the corrections that arise at one loop when integrating out heavy fields in supersymmetric models. We show that, in type-I see-saw models, complex A and B terms of the heavy right-handed neutrino give radiative contributions to the neutron EDM, as well as new dominant contributions to the electron EDM. Type-II and type-III see-saw also predict a pure gauge correction that makes complex the masses of the weak gauginos. All the see-saw models can predict observable EDM for the electron and for the neutron in a peculiar ratio.

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arXiv2010

Slepton mass-splittings as a signal of LFV at the LHC

Precise measurements of slepton mass-splittings might represent a powerful tool to probe supersymmetric (SUSY) lepton flavour violation (LFV) at the LHC. We point out that mass-splittings of the first two generations of sleptons are especially sensitive to LFV effects involving $τ-μ$ transitions. If these mass-splittings are LFV induced, high-energy LFV processes like the neutralino decay ${\nt}_2\to\nt_1τ^{\pm}μ^{\mp}$ as well as low-energy LFV processes like $τ\toμγ$ are unavoidable. We show that precise slepton mass-splitting measurements and LFV processes both at the high- and low-energy scales are highly complementary in the attempt to (partially) reconstruct the flavour sector of the SUSY model at work. The present study represents another proof of the synergy and interplay existing between the LHC, i.e. the {\em high-energy frontier}, and high-precision low-energy experiments, i.e. the {\em high-intensity frontier}.

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arXiv2010

The SUSY CP Problem and the MFV Principle

We address the SUSY CP problem in the framework of Minimal Flavor Violation (MFV), where the SUSY flavor problem finds a natural solution. By contrast, the MFV principle does not solve the SUSY CP problem as it allows for the presence of new {\it flavor blind} CP-violating phases. Then, we generalize the MFV ansatz accounting for a natural solution of it. The phenomenological implications of the generalized MFV ansatz are explored for MFV scenarios defined both at the electroweak (EW) and at the GUT scales.

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arXiv2010

A Lower Bound on hadronic EDMs from CP Violation in D0-D0bar mixing in SUSY Alignment Models

The SM predictions for CP violating effects in D meson systems are highly suppressed at the per mill level. Therefore, any experimental evidence for a sizable CP violation in D0-D0bar mixing would unambiguously point towards a New Physics (NP) signal. Within supersymmetric scenarios, the popular alignment models can naturally account for large, non-standard effects in D0-D0bar mixing. We demonstrate that, within alignment models, detectable CP violating effects in D0-D0bar mixing would unambiguously imply a lower bound for the electric dipole moment (EDM) of hadronic systems, like the neutron EDM and the mercury EDM, in the reach of future experimental sensitivities. The simultaneous evidence of CP violation in D meson systems together with non vanishing hadronic EDMs would strongly support the idea of SUSY alignment models and disfavour gauge-mediated SUSY breaking models, SUSY models with MFV and non-Abelian SUSY flavour models. As a byproduct of our analysis, we study the correlation between the time dependent CP asymmetry in decays to CP eigenstates S_f and the semileptonic asymmetry a_SL both model independently and in SUSY alignment models.

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arXiv2008

A Complete Analysis of "Flavored" Electric Dipole Moments in Supersymmetric Theories

The Standard Model predictions for the hadronic and leptonic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics effects. Especially, within supersymmetric frameworks with flavor-violating soft terms large and potentially visible effects to the EDMs are typically expected. In this work, we systematically evaluate the predictions for the EDMs at the beyond-leading-order (BLO). In fact, we show that BLO contributions to the EDMs dominate over the leading-order (LO) effects in large regions of the supersymmetric parameter space. Hence, their inclusion in the evaluation of the EDMs is unavoidable. As an example, we show the relevance of BLO effects to the EDMs for a SUSY $SU(5)$ model with right-handed neutrinos.

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arXiv2008

Running minimal flavor violation

We consider the flavor structure of the minimal supersymmetric standard model (MSSM) in the framework of `minimal flavor violation' (MFV). We show that, if one imposes the MFV structure at some scale, to a good accuracy the MFV decomposition works at all other scales. That is, quantum effects can be described by running coefficients of the MFV decomposition. We find that the coefficients get driven to non-trivial fixed points.

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arXiv2008

Light charged Higgs at the beginning of the LHC era

The terascale will be explored with the start of the LHC. One of the most fundamental questions which we expect to be answered is the root of electroweak symmetry breaking and whether the Higgs mechanism is realized in nature or not. In this context we pose the question if existing experimental data still allow for a light non-minimal Higgs sector. We tackle this question first in the context of the two Higgs doublet model and then we concentrate in two supersymmetric models, the constrained MSSM and the MSSM with non-universal Higgs masses. In both supersymmetric scearios, light pseudoscalar and light charged-Higgs bosons are still viable provided tan beta is large. In this regime, we emphasize the importance of the constraints provided by the decay B to tau nu mediated by the charged-Higgs at tree-level. In addition we comment on generic predictions for hadronic colliders and indirect searches in such scenarios.

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arXiv2007

Flavour physics at large tan(beta) with a Bino-like LSP

The MSSM with large tan(beta) and heavy squarks is a theoretically well motivated and phenomenologically interesting extension of the SM. This scenario naturally accommodates the (g-2)_μanomaly and the upper bound on the Higgs boson mass. In a wide region of the parameter space, visible non-standard effects are expected in a few low-energy observables, such as BR(B->tau nu), BR(B->l+ l-), BR(B->Xs gamma), and BR(mu->e gamma). We analyse the correlations of these non-standard effects under the additional assumption that the relic density of a Bino-like LSP accommodates the observed dark matter distribution.

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arXiv2007

Hints of large tan(beta) in flavour physics

Motivated by the first evidence of the B -> tau nu transition reported by Belle and by the precise DeltaM_{B_s} measurement by CDF, we analyse these and other low-energy observables in the framework of the MSSM at large tan(beta). We show that for heavy squarks and A terms (M_squarks, A_U > 1 TeV) such scenario has several interesting virtues. It naturally describes: i) a suppression of BR(B->tau nu) of (10-40)%, ii) a sizable enhancement of (g-2)_mu, iii) a heavy SM-like Higgs (m_h ~ 120 GeV), iv) small non-standard effects in DeltaM_{B_s} and BR(B -> X_s gamma) (in agreement with present observations). The possibilities to find more convincing evidences of such scenario, with improved data on BR(B -> tau nu), BR(B -> l+ l-) and other low-energy observables, are briefly discussed.

hep-ph↗

arXiv2007

Flavor Physics in SUSY at large tan(beta)

We discuss the phenomenological impact of a particularly interesting corner of the MSSM: the large tan(beta) regime. The capabilities of leptonic and hadronic Flavor Violating processes in shedding light on physics beyond the Standard Model are reviewed. Moreover, we show that tests of Lepton Universality in charged current processes can represent an interesting handle to obtain relevant information on New Physics scenarios.

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arXiv2006

New Two-loop Contributions to Hadronic EDMs in the MSSM

Flavor-changing terms with CP-violating phases in the quark sector may contribute to the hadronic electric dipole moments (EDMs). However, within the Standard Model (SM), the source of CP violation comes from the unique CKM phase, and it turns out that the EDMs are strongly suppressed. This implies that the EDMs are very sensitive to non-minimal flavor violation structures of theories beyond the SM. In this paper, we discuss the quark EDMs and CEDMs (chromoelectric dipole moments) in the MSSM with general flavor-changing terms in the squark mass matrices. In particular, the charged-Higgs mediated contributions to the down-quark EDM and CEDM are evaluated at two-loop level. We point out that these two-loop contributions may dominate over the one-loop induced gluino or Higgsino contributions even when the squark and gluino masses are around few TeV and \tanβis moderate.

hep-ph↗

arXiv2006

Exploring the flavour structure of the MSSM with rare K decays

We present an extensive analysis of rare K decays, in particular of the two neutrino modes K+->pi+ nu nu-bar and KL->pi0 nu nu-bar, in the Minimal Supersymmetric extension of the Standard Model. We analyse the expectations for the branching ratios of these modes, both within the restrictive framework of the minimal flavour violation hypothesis and within a more general framework with new sources of flavour-symmetry breaking. In both scenarios, the information that can be extracted from precise measurements of the two neutrino modes turn out to be very useful in restricting the parameter space of the model, even after taking into account the possible information on the mass spectrum derived from high-energy colliders, and the constraints from B-physics experiments. In the presence of new sources of flavour-symmetry breaking, additional significant constraints on the model can be derived also from the two KL->pi0 l+l- modes.

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arXiv2006

Higgs-Mediated tau --> mu and tau --> e transitions in II Higgs doublet Model and Supersymmetry

We study the phenomenology of the mu-tau and e-tau lepton flavour violation (LFV) in a general two Higgs Doublet Model (2HDM) including the supersymmetric case. We consider several LFV decay modes of the charged fermion tau, namely tau-> l_jgamma, tau->l_j l_k l_k and tau-> l_jeta. The predictions and the correlations among the rates of the above processes are computed. In particular, it is shown that tau->l_jgamma processes are the most sensitive channels to Higgs-mediated LFV specially if the splitting among the neutral Higgs bosons masses is not below the 10% level.

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arXiv2005

Constraints on SUSY Lepton Flavour Violation by rare processes

We study the constraints on flavour violating terms in low energy SUSY coming from several processes as li -> lj gamma, li -> lj lj lj and mu -> e in Nuclei. We show that a combined analysis of the processes allows us to extract additional information with respect to an individual analysis of all the processes. In particular, it makes possible to put bounds on sectors previously unconstrained by li -> lj gamma. We perform the analysis both in the mass eigenstate and in the mass insertion approximations clarifying the limit of applicability of these approximations.

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