10678678
Decoupling or nondecoupling: Is that the R($b$) question?
The top quark is well known for the nondecoupling effects it implies in ρ and Rb. The recent experimental Rb data exhibits a disagreement with the SM prediction at more than the 3σ level. It is tempting to explore whether this might be due to nondecoupling New Physics effects, opposite to those of the top. We investigate this issue in the context of models with an extra family of right or left handed, singlet or doublet quarks. It is shown that, contrary to what
18820051
Natural masslessness conservation for neutrinos in two-Higgs-doublet models.
We present a model which supplements the standard electroweak model with three right-handed neutrinos and one extra scalar doublet which does not develop a vacuum expectation value. With the aid of a discrete symmetry the neutrinos are kept strictly massless. This model has several interesting features. It has unsuppressed lepton flavor violating processes, in particular [mu][r arrow][ital e][gamma], hinting at the possibility that these may soon be within experimental reach. The [ital Z] and [ital W] interactions become nondiagonal at one-loop level. In particular, a nontrivial leptonic mixing matrix is seen to arise from the clash between the charged gauge boson and the charged scalar interactions.
17876300
Detecting new physics from CP violating phase measurements in B decays
The standard CKM model can be tested and New Physics detected using only CP-violating phase measurements in B decays. This requires the measurement of a phase factor which is small in the Standard Model, in addition to the usual large phases $\beta$ and $\gamma$. We also point out that identifying violations of the unitarity of the CKM matrix is rather difficult, and cannot be done with phase measurements alone.
1040688
Constraining new interactions with leptonic tau decays.
The recent measurements of the Michel parameters in {tau} decays enable, for the first time, a thorough analysis of the leptonic sector. In general, in models beyond the standard model, these parameters will be altered through changes in the {ital W} and {ital Z} couplings, and/or through interactions mediated by new gauge bosons. We perform a complete, model-independent analysis of the constraints imposed by the present data on such boson-mediated interactions, and point out the existence of useful relations among the couplings.
117893999
Looking for Delta I = 5/2 amplitude components in B ---> pi pi and B -> rho rho experiments
We discuss how experiments measuring B -> pi pi and B -> rho rho may be used to search for a Delta I = 5/2 amplitude component. This component could be the explanation for a recent (albeit very tentative) hint from B(Bbar) -> rho rho decays that the isospin triangles do not close.
5996250
Determining the penguin effect on CP violation in B0--> pi + pi -
A major goal in B physics is measuring the CP-violating asymmetry in the decay B → ππ. In order to determine one of the phase angles in the CKM matrix from this decay it is necessary to determine the influence of the penguin amplitude. Here we show how, using SU(3) symmetry, the penguin effect can be approximately determined from the ratio of the decay rates of B → Kπ and B → ππ. Recently evidence has been presented for the decays B̄ → ππ and B̄ → πK with a combined branching ratio of 2×10 [1]. The decay B̄ → ππ is of particular interest since it is one of the prime candidates for the study of CP violation in B decays. From the sudy of CP violation in B decays, one can determine the phases γ and β of the CKM matrix [2], defined by Vub = Aλ [ρ − iη] = Aλze , (1) Vtd = Aλ [(1 − ρ) − iη] = Aλye , (2) where y = √ (1 − ρ) + η = (cos γ + sin γ/ tanβ) , (3) z = √ ρ + η = (cos β + sin β/ tan γ) . (4) The decay asymmetry for B → ΨKs determines the angle β and, in the tree approximation, the decay asymmetry for B → ππ determines (β + γ). However, a number of authors [3] have emphasized that there may be a sizeable uncertain penguin contribution to the B̄ → ππ decay, thus making the determination of (β + γ) uncertain. Here we show that the approximate SU(3) symmetry can be used to estimate this penguin contribution once the ratio of πK to ππ is determined. The effective hamiltonian responsible for these decays is [4] Heff = 2 √ 2GF [ξ α u (C1O 1 + C2O 2 ) + ξ t 6
118653712
Notes on the two-brane model with variable tension
Motivated by possible extensions of the braneworld models with two branes, we investigate some consequences of a variable brane tension, using the well established results on consistency conditions. By a slight modification of the usual stress-tensor used in order to derive the braneworld sum rules, we find some important constraints obeyed by time-dependent brane tensions. In particular, it is shown that the tensions of two Randall-Sundrum\char21{}like branes obeying, at the same time, an E\"otv\"os law, aggravate the fine-tuning problem. Also, it is shown that if the hidden brane tension obeys an E\"otv\"os law, then the visible brane has a mixed behavior allowing a bouncinglike period at early times while it is dominated by an E\"otv\"os law now. To finalize, we discuss some qualitative characteristics, which may arise in the scope of dynamical brane tensions, as anisotropic background and branons production.
56092735
Two-branes with variable tension model and the effective Newtonian constant
It is shown that, in the two brane time variation model framework, if the hidden brane tension varies according to the phenomenological Eoetvoes law, the visible brane tension behavior is such that its time derivative is negative in the past and positive after a specific time of cosmological evolution. This behavior is interpreted in terms of a useful mechanical system analog and its relation with the variation of the Newtonian (effective) gravitational ''constant'' is explored.
119241024
PAMELA and FERMI limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques have reached important milestones with the precise measurements of the anti-proton () and gamma-ray spectra, notably by the PAMELA and FERMI-LAT experiments. While the γ-ray results have been used to test the thermal Dark Matter hypothesis and constrain the Dark Matter annihilation cross section into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA experiment remains relatively unexploited. Here we show that the latter can be used to set a constraint on the neutralino-chargino mass difference. To illustrate our point we use a Supersymmetric model in which the gauginos are light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP) is the neutralino. In this framework the W+W− production is expected to be significant, thus leading to large and γ-ray fluxes. After determining a generic limit on the Dark Matter pair annihilation cross section into W+W− from the data only, we show that one can constrain scenarios in which the neutralino-chargino mass difference is as large as 20 GeV for a mixed neutralino (and intermediate choices of the propagation scheme). This result is consistent with the limit obtained by using the FERMI-LAT data. As a result, we can safely rule out the pure wino neutralino hypothesis if it is lighter than 450 GeV and constitutes all the Dark Matter.
115163234
ELKO, Flagpole and Flag-Dipole Spinor Fields, and the Instanton Hopf Fibration
Abstract.In a previous paper we explicitly constructed a mapping that leads Dirac spinor fields to the dual-helicity eigenspinors of the charge conjugation operator (ELKO spinor fields). ELKO spinor fields are prime candidates for describing dark matter, and belong to a wider class of spinor fields, the so-called flagpole spinor fields, corresponding to the class-(5), according to Lounesto spinor field classification, based on the relations and values taken by their associated bilinear covariants. Such a mapping between Dirac and ELKO spinor fields was obtained in an attempt to extend the Standard Model in order to encompass dark matter. Now we prove that such a mapping, analogous to the instanton Hopf fibration map S3...S7 → S4, indicates that ELKO is not suitable to describe the instanton. We review ELKO spinor fields as type-(5) spinor fields under the Lounesto spinor field classification, explicitly computing the associated bilinear covariants. This paper is also devoted to investigate some formal aspects of the flag-dipole spinor fields, which correspond to the class-(4) under the Lounesto spinor field classification and, in addition, we prove that type-(4) spinor fields — corresponding to flag-dipoles — and ELKO spinor fields — corresponding to flagpoles — can also be entirely described in terms of the Majorana and Weyl spinor fields. After all, by choosing a projection endomorphism of the spacetime algebra $${\mathcal C}\ell_{1,3}$$ it is shown how to obtain ELKO, flagpole, Majorana and Weyl spinor fields, respectively corresponding to type-(5) and -(6) spinor fields, uniquely from limiting cases of a type-(4) — flag-dipole — spinor field, in a similar result obtained by Lounesto.
119136375
Unfolding physics from the algebraic classification of spinor fields
Abstract After reviewing the Lounesto spinor field classification, according to the bilinear covariants associated to a spinor field, we call attention and unravel some prominent features involving unexpected properties about spinor fields under such classification. In particular, we pithily focus on the new aspects — as well as current concrete possibilities. They mainly arise when we deal with some non-standard spinor fields concerning, in particular, their applications in physics.