8 research outputs found
Composite fermions in Electroweak Symmetry Breaking
If the electroweak symmetry is broken by some unspecified strong dynamics,
composite fermions may exist with definite transformation properties under
SU(2)_L x SU(2)_R/SU(2)_{L+R} and may play a role in giving masses by mixing to
all the standard quarks and leptons. Assuming this to be the case, we analyze
the role of Singlets, Doublets and Triplets in the ElectroWeak Precision Tests
and in Flavour Physics. Doublets and Triplets are generically disfavoured. In
the Singlet case, we specify the breaking patterns of the flavour group that
allow to keep the CKM picture of flavour physics and we discuss the effects of
the mixing between composite and elementary fermions. These mixings affect in
particular the rather peculiar LHC phenomenology of the composite fermions.Comment: 18 pages, 2 figures (v2: minor modifications, published version
Probing Yukawa Unification with K and B Mixing
We consider corrections to the unification of down-quark and charged-lepton
Yukawa couplings in supersymmetric GUTs, which links the large nu_tau-nu_mu
mixing angle to b -> s transitions. These corrections generically occur in
simple grand-unified models with small Higgs representations and affect s -> d
and b -> d transitions via the mixing of the corresponding right-handed
superpartners. On the basis of a specific SUSY-SO(10) model, we analyze the
constraints from K-Kbar and B-Bbar mixing on the additional
\tilde{d}_R-\tilde{s}_R rotation angle theta. We find that epsilon_K already
sets a stringent bound on theta, theta^{max}=O(1 degree), indicating a very
specific flavor structure of the correction operators. The impact of the large
neutrino mixings on the unitarity triangle analysis is also briefly discussed,
as well as their ability to account for the sizeable CP-violating phase
observed recently in B_s -> psi phi decays.Comment: 19 pages. Discussion in Sec. 5.2 slightly extended; minor numerical
modifications in Secs. 5.1 to 5.4, conclusions unchanged. Version to appear
in JHE
Precision tests of the Standard Model with leptonic and semileptonic kaon decays
We present a global analysis of leptonic and semileptonic kaon decays data,
including all recent results by BNL-E865, KLOE, KTeV, ISTRA+, and NA48.
Experimental results are critically reviewed and combined, taking into account
theoretical (both analytical and numerical) constraints on the semileptonic
kaon form factors. This analysis leads to a very accurate determination of Vus
and allows us to perform several stringent tests of the Standard Model
Light neutralino in the MSSM: An update with the latest LHC results
We discuss the scenario of light neutralino dark matter in the minimal
supersymmetric standard model, which is motivated by the results of some of the
direct detection experiments --- DAMA, CoGENT, and CRESST. We update our
previous analysis with the latest results of the LHC. We show that new LHC
constraints disfavour the parameter region that can reproduce the results of
DAMA and CoGENT.Comment: 4 pages, 4 figures, to appear in the conference proceedings of TAUP
2011, Munich Germany, 5-9 September 201
Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu
The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been
used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at
CLEO-c and the B factories suggest a branching ratio for both decays somewhat
higher than the Standard Model prediction using f_D(s) from unquenched lattice
calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model
(Type II) would also mediate these decays, but any sizeable contribution from
H+- can only suppress the branching ratios and consequently is now slightly
disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+-
from such decays can be competitive with and complementary to analogous
constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+-
-> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) <
250 MeV.Comment: 18 pages, 4 figure
New strategies for New Physics search in B -> K* nu anti-nu, B -> K nu anti-nu and B -> X(s) nu anti-nu decays
The rare decay B -> K* nu anti-nu allows a transparent study of Z penguin and
other electroweak penguin effects in New Physics (NP) scenarios in the absence
of dipole operator contributions and Higgs (scalar) penguin contributions that
are often more important than Z contributions in B -> K* l+l- and B(s) -> l+l-
decays. We present a new analysis of B -> K* nu anti-nu with improved form
factors and of the decays B -> K nu anti-nu and B -> X(s) nu anti-nu in the SM
and in a number of NP scenarios like the general MSSM, general scenarios with
modified Z/Z' penguins and in a singlet scalar extension of the SM. We also
summarize the results in the Littlest Higgs model with T-parity and a
Randall-Sundrum (RS) model with custodial protection of left-handed Z-di-dj
couplings. Our SM prediction BR(B -> K* nu anti-nu)=(6.8^+1.0_-1.1) x 10^-6
turns out to be significantly lower than the ones present in the literature.
Our improved calculation BR(B -> X(s) nu anti-nu)=(2.7+-0.2) x 10^-5 in the SM
avoids the normalization to the BR(B -> X(c) e anti-nu(e)) and, with less than
10% total uncertainty, is the most accurate to date. The results for the SM and
NP scenarios can be transparently summarized in a (epsilon,eta) plane with a
non-vanishing eta signalling the presence of new right-handed down-quark
flavour violating couplings which can be ideally probed by the decays in
question. Measuring the three branching ratios and one additional polarization
observable in B -> K* nu anti-nu allows to overconstrain the resulting point in
the (epsilon,eta) plane with (epsilon,eta)=(1,0) corresponding to the SM. The
correlations of these three channels with the rare decays K+ -> pi+ nu anti-nu,
KL -> pi0 nu anti-nu, B -> X(s) l+ l- and B(s) -> mu+ mu- offer powerful tests
of New Physics with new right-handed couplings and non-MFV interactions.Comment: 31 pages, 14 figures, 3 tables. v2: 9 references, minor
clarifications and corrections added. Conclusions unchange
Measurement of the absolute branching ratios for semileptonic K+/- decays with the KLOE detector
Using a sample of over 600 million phi->K+K- decays collected at the Dafne
e+e- collider, we have measured with the KLOE detector the absolute branching
ratios for the charged kaon semileptonic decays, K+/- -> p0 e nu (gamma) (Ke3)
and K+/- -> p0 mu nu (gamma) (Kmu3). The results, BR(Ke3) = 0.04965 +/-
0.00038_{stat} +/- 0.00037_{syst} and BR(Kmu3) = 0.03233 +/- 0.00029_{stat} +/-
0.00026_{syst}, are inclusive of radiation. Accounting for correlations, we
derive the ratio Kmu3/Ke3 = 0.6511+/-0.0064. Using the semileptonic form
factors measured in the same experiment, we obtain V_{us}f_{+}(0) = 0.2141 +/-
0.0013.Comment: 13 pages, 3 figures, submitted to JHEP. v2: minor revisions required
by JHEP, v3: final version published by JHEP (replacement of 2 incorrect
affiliations)link: http://www.iop.org/EJ/abstract/1029-8479/2008/02/09
Pseudoscalar decay constants of kaon and D-mesons from = 2 twisted mass Lattice QCD
We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants fπ, fK, fD and fDs, performed with Nf = 2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. We have considered for the final analysis three values of the lattice spacing, a simeq 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to mπ simeq 270 MeV. Our results for the light meson decay constants are fK = 158.1(2.4) MeV and fK/fπ = 1.210(18). From the latter ratio, by using the experimental determination of Γ(K → μbar nuμ(γ))/Γ(π → μbar nuμ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2222(34), in good agreement with the determination from semileptonic Kl3 decays and the unitarity constraint. For the D and Ds meson decay constants we obtain fD = 197(9) MeV, fDs = 244(8) MeV and fDs/fD = 1.24(3). Our result for fD is in good agreement with the CLEO experimental measurement. For fDs our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4 σ level.We thank all the members of the ETM Collaboration for fruitful discussions. D.P. thanks the Dipartimento di Fisica,Universita di Roma Tre, and C.T. thanks the Laboratoire de Physique Th´eorique , Universite de Paris XI, for the hospitality. V.L., R.F., F.M. and S.S thank MIUR (Italy) for partial financial support under the contract PRIN06. D.P. thanks MEC (Spain) for partial financial support under grant FPA2005-00711. This work has been supported in part by the EU Contract No. MRTN-CT-2006-035482, “FLAVIAnet”and by the DFG Sonderforschungsbereich/Transregio SFB/TR9-03. We also acknowledge
the Consolider-Ingenio 2010 Program CPAN (CSD2007-00042).Peer reviewe