Gauging U(1) symmetries and the number of right-handed neutrinos

In this letter we consider that assuming: a) that the only left-handed neutral fermions are the active neutrinos, b) that $B-L$ is a gauge symmetry, and c) that the $L$ assignment is restricted to the integer numbers, the anomaly cancellation imply that at least three right-handed neutrinos must be added to the minimal representation content of the electroweak standard model. However, two types of models arise: i) the usual one where each of the three identical right-handed neutrinos has total lepton number L=1; ii) and the other one in which two of them carry L=4 while the third one carries $L=-5$.Comment: Published version in PLB forma

Unparticle Physics and A_{FB}^b on the Z pole

An attempt has been made to address the 3\sigma anomaly of the forward-backward asymmetry of b quark in LEP data via an unparticle sector. For most part of the parameter space except certain particular regions, the anomaly could not be explained away plausibly, when constraints from other LEP observables are taken into account.Comment: Version to appear in Phys. Lett. B. 13 pages, 5 figure

The Higgs resonance shape in gluon fusion: Heavy Higgs effects

We study the influence of two--loop radiative corrections of enhanced electroweak strength on Higgs production at the LHC. We consider Higgs production by the gluon fusion mechanism, with the subsequent decay of the Higgs boson into a pair of Z bosons, and incorporate the resonance shape corrections up to order $(g^2 \, m_H^2 / m_W^2)^2$. We take into account the full $g g \rightarrow Z Z$ process and the $q \bar{q} \rightarrow Z Z$ background, as well as the subsequent decay of the Z pair into leptons. We also discuss the theoretical uncertainty related to the use of the equivalence theorem in this process

Constraints on Quartic Vector-Boson Interactions from Z Physics

We obtain the constraints on possible anomalous quartic vector-boson vertices arising from the precision measurements at the $Z$ pole. In the framework of $SU(2)_L \otimes U(1)_Y$ chiral Lagrangians, we examine all effective operators of order $D=4$ that lead to four-gauge-boson interactions but do not induce anomalous trilinear vertices. We constrain the anomalous quartic interactions by evaluating their one-loop corrections to the $Z$ pole physics. Our analysis is performed in a generic $R_\xi$ gauge and it shows that only the operators that break the $SU(2)_C$ custodial symmetry get limits close to the theoretical expectations. Our results also indicate that these anomalous couplings are already out of reach of the Next Linear $e^+ e^-$ Collider, while the Large Hadron Collider could be able to further extend the bounds on some of these couplings.Comment: 16 pages, 1 Postscript figures, uses RevTex and eps.st

Multi-Scalar-Singlet Extension of the Standard Model - the Case for Dark Matter and an Invisible Higgs Boson

We consider a simple extension of the Standard Model by the addition of N real scalar gauge singlets \vp that are candidates for Dark Matter. By collecting theoretical and experimental constraints we determine the space of allowed parameters of the model. The possibility of ameliorating the little hierarchy problem within the multi-singlet model is discussed. The Spergel-Steinhardt solution of the Dark Matter density cusp problem is revisited. It is shown that fitting the recent CRESST-II data for Dark Matter nucleus scattering implies that the standard Higgs boson decays predominantly into pairs of Dark Matter scalars. It that case discovery of the Higgs boson at LHC and Tevatron is impossible. The most likely mass of the dark scalars is in the range 15 GeV \lsim \mvp \lsim 50 GeV with BR(h \to \vp\vp) up to 96%.Comment: 18 pages, 15 figure

LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector

We present a unified analysis of the two main production processes of vector boson pairs at the LHC, VV-fusion and qqbar annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final V_L V_L strong rescattering effects by a form factor, we describe qqbar annihilation processes in terms of the two chiral parameters that govern elastic V_L V_L scattering. Depending on the values of these two chiral parameters, the unitarized amplitudes may present resonant enhancements in different angular momentum-isospin channels. Scanning this two parameter space, we generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the LHC.Comment: Final version to appear in Phys. Rev. D, including a more detailed exposition and a few more references. Conclusions and results unchanged. 14 pages, 5 figure

Unravelling the WWγWW\gamma and WWZWWZ Vertices at the Linear Collider: νˉνγ\bar{\nu} \nu\gamma and νˉνqˉq\bar{\nu}\nu\bar{q}q final states

We perform a detailed analysis of the processes $e^+e^- \rightarrow \bar{\nu} \nu\gamma$ and $\bar{\nu}\nu\bar{q}q$ at future linear $e^+e^-$ colliders and assess their sensitivity to anomalous gauge boson couplings. We consider center of mass energies $\sqrt{s}=$ 350, 500 and 800 GeV. We demonstrate that significant improvements can be obtained if the phase space information for the cross sections is used maximally. At 800 GeV the parameters $\Delta\kappa_{\gamma}$ and $\lambda_{\gamma}$ can be constrained, at 95\% CL, to about 0.02 and 0.01, while the parameters $\Delta\kappa_Z$, $\lambda_Z$ and $\Delta g_1^Z$ can be probed down to about 0.009, 0.002 and 0.004 respectively. The precision of these measurements is likely to be limited by statistical errors at anticipated luminosities at these energies.Comment: LaTeX, 16 pages, 7 figs (embedded

The Higgs resonance in vector boson scattering

A heavy Higgs resonance is described in a representation-independent way which is valid for the whole energy range of 2 -> 2 scattering processes, including the asymptotic behavior at low and high energies. The low-energy theorems which follow from to the custodial SU_2 symmetry of the Higgs sector restrict the possible parameterizations of the lineshape that are consistent in perturbation theory. Matching conditions are specified which are necessary and sufficient to relate the parameters arising in different expansions. The construction is performed explicitly up to next-to-leading order.Comment: 25 pages, revtex, uses epsf, amssym

Design of the BRISC study: a multicentre controlled clinical trial to optimize the communication of breast cancer risks in genetic counselling

Background: Understanding risks is considered to be crucial for informed decision-making. Inaccurate risk perception is a common finding in women with a family history of breast cancer attending genetic counseling. As yet, it is unclear how risks should best be communicated in clinical practice. This study protocol describes the design and methods of the BRISC (Breast cancer RISk Communication) study evaluating the effect of different formats of risk communication on the counsellee's risk perception, psychological well-being and decision-making regarding preventive options for breast cancer. Methods and design: The BRISC study is designed as a pre-post-test controlled group intervention trial with repeated measurements using questionnaires. The intervention-an additional risk consultation-consists of one of 5 conditions that differ in the way counsellee's breast cancer risk is communicated: 1) lifetime risk in numerical format (natural frequencies, i.e. X out of 100), 2) lifetime risk in both numerical format and graphical format (population figures), 3) lifetime risk and age-related risk in numerical format, 4) lifetime risk and age-related risk in both numerical format and graphical format, and 5) lifetime risk in percentages. Condition 6 is the control condition in which no intervention is given (usual care). Participants are unaffected women with a family history of breast cancer attending one of three participating clinical genetic centres in the Netherlands. Discussion: The BRISC study allows for an evaluation of the effects of different formats of communicating breast cancer risks to counsellees. The results can be used to optimize risk communication in order to improve informed decision-making among women with a family history of breast cancer. They may also be useful for risk communication in other health-related services. Trial registration: Current Controlled Trials ISRCTNI4566836

Uses and Abuses of Effective Lagrangians

Motivated by past and recent analyses we critically re-examine the use of effective lagrangians in the literature to constrain new physics and to determine the `physics reach' of future experiments. We demonstrate that many calculations, such as those involving anomalous trilinear gauge-boson couplings, either considerably overestimate loop-induced effects, or give ambiguous answers. The source of these problems is the use of cutoffs to evaluate the size of such operators in loop diagrams. In contrast to other critics of these loop estimates, we prove that the inclusion of nonlinearly-realized gauge invariance into the low-energy lagrangian is irrelevant to this conclusion. We use an explicit example using known multi-Higgs physics above the weak scale to underline these points. We show how to draw conclusions regarding the nature of the unknown high-energy physics without making reference to low-energy cutoffs.Comment: 36 page