Measurements of neutral vector resonance in Higgsless models at the LHC

In Higgsless models, new vector resonances appear to restore the unitarity of the W_L W_L scattering amplitude without the Higgs boson. In the ideal delocalized three site Higgsless model, one of large prodcution cross section of the neutral vector resonance (Z') at the Large Hadron Collider is the W-associated production, pp \to Z'W \to WWW. Although the dileptonic decay channnel, l\nu l'\nu 'jj, is experimentally clean to search for the Z' signals, it is difficult to reconstruct the Z' invariant mass due to the two neutrinos in the final state. We study collider signatures of Z' using the M_{T2}-Assisted On-Shell (MAOS) reconstruction of the missing neutrino momenta. We show the prospect of the Z' mass determination in the channel, l\nu l'\nu 'jj, at the Large Hadron Collider.Comment: 16 pages, 6 figures, 5 tables; v2: references added, minor corrections, version published in JHE

R-parity violating resonant stop production at the Large Hadron Collider

We have investigated the resonant production of a stop at the Large Hadron Collider, driven by baryon number violating interactions in supersymmetry. We work in the framework of minimal supergravity models with the lightest neutralino being the lightest supersymmetric particle which decays within the detector. We look at various dilepton and trilepton final states, with or without b-tags. A detailed background simulation is performed, and all possible decay modes of the lighter stop are taken into account. We find that higher stop masses are sometimes easier to probe, through the decay of the stop into the third or fourth neutralino and their subsequent cascades. We also comment on the detectability of such signals during the 7 TeV run, where, as expected, only relatively light stops can be probed. Our conclusion is that the resonant process may be probed, at both 10 and 14 TeV, with the R-parity violating coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The possibility of distinguishing between resonant stop production and pair-production is also discussed.Comment: 20 pages, 4 figures, 6 tables; Version accepted by JHE

Light neutralino dark matter in the MSSM and its implication for LHC searches for staus

It was shown in a previous study that a lightest neutralino with mass below 30 GeV was severely constrained in the minimal supersymmetric standard model (MSSM), unless it annihilates via a light stau and thus yields the observed dark matter abundance. In such a scenario, while the stau is the next-to-lightest supersymmetric particle (NLSP), the charginos and the other neutralinos as well as sleptons of the first two families are also likely to be not too far above the mass bounds laid down by the Large Electron Positron (LEP) collider. As the branching ratios of decays of the charginos and the next-to-lightest neutralino into staus are rather large, one expects significant rates of tau-rich final states in such a case. With this in view, we investigate the same-sign ditau and tri-tau signals of this scenario at the Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to light neutralino dark matter. The associated signal rates for these channels are computed, for the centre-of-mass energy of 14 TeV. We find that both channels lead to appreciable rates if the squarks and the gluino are not too far above a TeV, thus allowing to probe scenarios with light neutralinos in the 14 TeV LHC run with 10-100 fb^{-1}.Comment: 19p, 4 Fig

Muon to electron conversion in the Littlest Higgs model with T-parity

Little Higgs models provide a natural explanation of the little hierarchy between the electroweak scale and a few TeV scale, where new physics is expected. Under the same inspiring naturalness arguments, this work completes a previous study on lepton flavor-changing processes in the Littlest Higgs model with T-parity exploring the channel that will eventually turn out to be the most sensitive, \mu-e conversion in nuclei. All one-loop contributions are carefully taken into account, results for the most relevant nuclei are provided and a discussion of the influence of the quark mixing is included. The results for the Ti nucleus are in good agreement with earlier work by Blanke et al., where a degenerate mirror quark sector was assumed. The conclusion is that, although this particular model reduces the tension with electroweak precision tests, if the restrictions on the parameter space derived from lepton flavor violation are taken seriously, the degree of fine tuning necessary to meet these constraints also disfavors this model.Comment: 26 pages, 7 figures, 4 tables; discussion improved, results unchanged, one reference added, version to appear in JHE

Bridging flavour violation and leptogenesis in SU(3) family models

We reconsider basic, in the sense of minimal field content, Pati-Salam x SU(3) family models which make use of the Type I see-saw mechanism to reproduce the observed mixing and mass spectrum in the neutrino sector. The goal of this is to achieve the observed baryon asymmetry through the thermal decay of the lightest right-handed neutrino and at the same time to be consistent with the expected experimental lepton flavour violation sensitivity. This kind of models have been previously considered but it was not possible to achieve a compatibility among all of the ingredients mentioned above. We describe then how different SU(3) messengers, the heavy fields that decouple and produce the right form of the Yukawa couplings together with the scalars breaking the SU(3) symmetry, can lead to different Yukawa couplings. This in turn implies different consequences for flavour violation couplings and conditions for realizing the right amount of baryon asymmetry through the decay of the lightest right-handed neutrino. Also a highlight of the present work is a new fit of the Yukawa textures traditionally embedded in SU(3) family models.Comment: 26 pages, 5 figures, Some typos correcte

Rare B Decays with a HyperCP Particle of Spin One

In light of recent experimental information from the CLEO, BaBar, KTeV, and Belle collaborations, we investigate some consequences of the possibility that a light spin-one particle is responsible for the three Sigma^+ -> p mu^+ mu^- events observed by the HyperCP experiment. In particular, allowing the new particle to have both vector and axial-vector couplings to ordinary fermions, we systematically study its contributions to various processes involving b-flavored mesons, including B-Bbar mixing as well as leptonic, inclusive, and exclusive B decays. Using the latest experimental data, we extract bounds on its couplings and subsequently estimate upper limits for the branching ratios of a number of B decays with the new particle. This can serve to guide experimental searches for the particle in order to help confirm or refute its existence.Comment: 17 pages, 3 figures; discussion on spin-0 case modified, few errors corrected, main conclusions unchange

Simultaneous Extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation

Several recent studies performed on constraints of a fourth generation of quarks and leptons suffer from the ad-hoc assumption that 3 x 3 unitarity holds for the first three generations in the neutrino sector. Only under this assumption one is able to determine the Fermi constant G_F from the muon lifetime measurement with the claimed precision of G_F = 1.16637 (1) x 10^-5 GeV^-2. We study how well G_F can be extracted within the framework of four generations from leptonic and radiative mu and tau decays, as well as from K_l3 decays and leptonic decays of charged pions, and we discuss the role of lepton universality tests in this context. We emphasize that constraints on a fourth generation from quark and lepton flavour observables and from electroweak precision observables can only be obtained in a consistent way if these three sectors are considered simultaneously. In the combined fit to leptonic and radiative mu and tau decays, K_l3 decays and leptonic decays of charged pions we find a p-value of 2.6% for the fourth generation matrix element |U_{e 4}|=0 of the neutrino mixing matrix.Comment: 19 pages, 3 figures with 16 subfigures, references and text added refering to earlier related work, figures and text in discussion section added, results and conclusions unchange

Constraints from muon g-2 and LFV processes in the Higgs Triplet Model

Constraints from the muon anomalous magnetic dipole moment and lepton flavor violating processes are translated into lower bounds on v_Delta*m_H++ in the Higgs Triplet Model by considering correlations through the neutrino mass matrix. The discrepancy of the sign of the contribution to the muon anomalous magnetic dipole moment between the measurement and the prediction in the model is clarified. It is shown that mu to e gamma, tau decays (especially, tau to mu e e), and the muonium conversion can give a more stringent bound on v_Delta*m_H++ than the bound from mu to eee which is expected naively to give the most stringent one.Comment: 18 pages, 16 figure

New physics searches at near detectors of neutrino oscillation experiments

We systematically investigate the prospects of testing new physics with tau sensitive near detectors at neutrino oscillation facilities. For neutrino beams from pion decay, from the decay of radiative ions, as well as from the decays of muons in a storage ring at a neutrino factory, we discuss which effective operators can lead to new physics effects. Furthermore, we discuss the present bounds on such operators set by other experimental data currently available. For operators with two leptons and two quarks we present the first complete analysis including all relevant operators simultaneously and performing a Markov Chain Monte Carlo fit to the data. We find that these effects can induce tau neutrino appearance probabilities as large as O(10^{-4}), which are within reach of forthcoming experiments. We highlight to which kind of new physics a tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX

Lepton Number Violation from Colored States at the LHC

The possibility to search for lepton number violating signals at the Large Hadron Collider (LHC) in the colored seesaw scenario is investigated. In this context the fields that generate neutrino masses at the one-loop level are scalar and Majorana fermionic color-octets of SU(3). Due to the QCD strong interaction these states may be produced at the LHC with a favorable rate. We study the production mechanisms and decays relevant to search for lepton number violation signals in the channels with same-sign dileptons. In the simplest case when the two fermionic color-octets are degenerate in mass, one could use their decays to distinguish between the neutrino spectra. We find that for fermionic octets with mass up to about 1 TeV the number of same-sign dilepton events is larger than the standard model background indicating a promising signal for new physics.Comment: minor corrections, added reference