106 research outputs found
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.Comment: 8 pages, 6 figures. V2: one comment added, published version in PL
On the Importance of Electroweak Corrections for B Anomalies
The growing experimental indication of Lepton Flavour Universality Violation
(LFUV) both in charged- and neutral-current semileptonic B-decays, has
triggered many theoretical interpretations of such non-standard phenomena.
Focusing on popular scenarios where the explanation of these anomalies requires
New Physics at the TeV scale, we emphasise the importance of including
electroweak corrections to obtain trustable predictions for the models in
question. We find that the most important quantum effects are the modifications
of the leptonic couplings of the W and Z vector bosons and the generation of a
purely leptonic effective Lagrangian. As a result, the tight experimental
bounds on Z-pole observables and tau decays challenge an explanation of the
current non-standard data. We illustrate how these effects arise, by providing
a detailed discussion of the running and matching procedure which is necessary
to derive the low-energy effective Lagrangian.Comment: 38 pages, 7 figures. V2: Text improvments. Published versio
Higgs--mediated K -> pi nu nu-bar in the MSSM at large tan(beta)
We analyze the impact of Higgs-mediated amplitudes on the rare decays KL ->
pi0 nu nu-bar and K+ -> pi+ nu nu-bar in the MSSM with large tan(beta) and
general flavour mixing. We point out that, going beyond the minimal flavour
violation hypothesis, Z-penguin amplitudes generated by charged-Higgs exchange
can induce sizable modifications of K -> pi nu nu-bar rates. Interestingly,
these effects scale as tan^4(beta) at the amplitude level. For large values of
tan(beta), this mechanism allows deviations from the SM expectations even for
tiny (CKM-type) off-diagonal mixing terms in the right-handed squark sector.Comment: 9 pages, 2 figure
Revisiting Lepton Flavour Universality in B Decays
Lepton flavour universality (LFU) in B-decays is revisited by considering a
class of semileptonic operators defined at a scale Lambda above the electroweak
scale v. The importance of quantum effects, so far neglected in the literature,
is emphasised. We construct the low-energy effective Lagrangian taking into
account the running effects from Lambda down to v through the one-loop
renormalization group equations (RGE) in the limit of exact electroweak
symmetry and QED RGEs from v down to the 1 GeV scale. The most important
quantum effects turn out to be the modification of the leptonic couplings of
the vector boson Z and the generation of a purely leptonic effective
Lagrangian. Large LFU breaking effects in Z and tau decays and visible lepton
flavour violating (LFV) effects in the processes tau -> mu ll, tau -> mu rho,
tau -> mu pi and tau -> mu eta^(') are induced.Comment: 5 pages, 2 figures. V2: Minor text improvements. Published PRL
versio
Lepton Flavour Violation in Composite Higgs Models
We discuss in detail the constraints on partial compositeness coming from
flavour and CP violation in the leptonic sector. In a first part we present a
formulation of partial compositeness in terms of a flavour symmetry group and a
set of spurions, whose background values specify the symmetry breaking pattern.
In such a framework we construct the complete set of dimension-six operators
describing lepton flavour violation and CP violation. By exploiting the
existing bounds, we derive limits on the compositeness scale in different
scenarios, characterised by increasing restrictions on the spurion properties.
We confirm that in the most general case the compositeness scale should lie
well-above 10 TeV. However, if in the composite sector mass parameters and
Yukawa couplings are universal, such a bound can be significantly lowered,
without necessarily reproducing the case of minimal flavour violation. The most
sensitive processes are decays of charged leptons either of radiative type or
into three charged leptons, muon to electron conversion in nuclei and the
electric dipole moment of the electron. In a second part we explicitly compute
the Wilson coefficients of the relevant dimension-six operators in the
so-called two-site model, embodying the symmetry breaking pattern discussed in
our first part, and we compare the results with those of the general spurion
analysis.Comment: 42 pages, 9 figures; text improved, some corrections in appendix B
and C, results unchange
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 \tan\beta is moderate.Comment: 13 pages, 6 figure
Lepton Flavor Violation in Flavored Gauge Mediation
We study the anatomy and phenomenology of Lepton Flavor Violation (LFV) in
the context of Flavored Gauge Mediation (FGM). Within FGM, the messenger sector
couples directly to the MSSM matter fields with couplings controlled by the
same dynamics that explains the hierarchies in the SM Yukawas. Although the
pattern of flavor violation depends on the particular underlying flavor model,
FGM provides a built-in flavor suppression similar to wave function
renormalization or SUSY Partial Compositeness. Moreover, in contrast to these
models, there is an additional suppression of left-right (LR) flavor
transitions by third-generation Yukawas that in particular provides an extra
protection against flavor-blind phases. We exploit the consequences of this
setup for lepton flavor phenomenology, assuming that the new couplings are
controlled by simple U(1) flavor models that have been proposed to accommodate
large neutrino mixing angles. Remarkably, it turns out that in the context of
FGM these models can pass the impressive constraints from LFV processes and
leptonic EDMs even for light superpartners, therefore offering the possibility
of resolving the longstanding muon g-2 anomaly.Comment: 32 pages, 7 figure
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.Comment: 15 pages, 4 figure
On the interrelationship among leptonic g - 2, EDMs and lepton flavor violation
We present a concise review of the status of charged lepton flavor violation (cLFV) in scenarios beyond the SM. We emphasize that the current experimental resolutions on cLFV processes are already testing territories of new physics (NP) models well beyond the LHC reach. On the other hand, with the expected sensitivities of next-generation experiments, cLFV will become the most powerful probe of NP signals at our disposal. Finally, the interrelationship among leptonic g â 2, EDMs and cLFV will turn out to be of outmost importance to disentangle among different NP scenarios
Probing the muon g-2 anomaly at a Muon Collider
The capability of a foreseen Muon Collider to probe the muon -2 is
systematically investigated. We demonstrate that a Muon Collider, running at
center-of-mass energies of several TeV, can provide the first model-independent
high-energy test of new physics in the muon -2, being sensitive to
deviations of few x 10^-9. This achievement would be of the utmost importance
to shed light on the long-standing muon -2 anomaly. Furthermore, we show
that the current bound on the muon electric dipole moment can be improved by
three orders of magnitude, down to few x 10^-22 e cm.Comment: 5 pages, 3 figures. v2: discussion on muon EDM added, references
updated, presentation improve
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