Search results for "ROWE"
showing 10 items of 842 documents
Precision measurement of the hadronic cross-section through the radiative return method
2002
Electron--positron annihilation into hadrons plus an energetic photon from initial-state radiation allows the hadronic cross-section to be measured over a wide range of energies at high luminosity meson factories. Weighted integrals over this cross-section are a decisive input for electroweak precision tests. A Monte Carlo event generator called PHOKHARA has been developed, which simulates $e^+ e^- \to$ hadrons + photon(s) at the NLO accuracy. The latest tests and upgrades are presented in this paper.
Implications of an axino LSP for naturalness
2014
Both the naturalness of the electroweak symmetry breaking and the resolution of the strong CP problem may require a small Higgsino mass $\mu$ generated by a realization of the DFSZ axion model. Assuming the axino is the lightest supersymmetric particle, we study its implications on $\mu$ and the axion scale. Copiously produced light Higgsinos at collider (effectively only neutral NLSP pairs) eventually decay to axinos leaving prompt multi-leptons or displaced vertices which are being looked for at the LHC. We use latest LHC7+8 results to derive current limits on $\mu$ and the axion scale. Various Higgsino-axino phenomenology is illustrated by comparing with a standard case without lightest …
CKM matrix and fermion masses in the dualized standard model
1997
A Dualized Standard Model recently proposed affords a natural explanation for the existence of Higgs fields and of exactly 3 generations of fermions, while giving at the same time the observed fermion mass hierarchy together with a tree-level CKM matrix equal to the identity matrix. It further suggests a method for generating from loop corrections the lower generation masses and nondiagonal CKM matrix elements. In this paper, the proposed calculation is carried out to 1-loop. It is found first that with the method suggested one can account readily for the masses of the second generation fermions as a `leakage' from the highest generation. Then, with the Yukawa couplings fixed by fitting the…
The tau weak-magnetic dipole moment
1994
We calculate the prediction for the anomalous weak-magnetic form factor of the tau lepton at $q^2=M_Z^2$ within the Standard Model. With all particles on-shell, this is a electroweak gauge invariant quantity. Its value is $a_\tau^w (M_Z^2)= - \;(2.10 + 0.61\, i) \times 10^{-6}$. We show that the transverse and normal components of the single-tau polarization of tau pairs produced at $e^+e^-$ unpolarized collisions are sensitive to the real and absorptive parts of the anomalous weak-magnetic dipole moment of the tau. The sensitivity one can achieve at LEP in the measurement of this dipole moment is discussed.
Lepton-number violation and right-handed neutrinos in Higgs-less effective theories
2005
Following previous work, we identify a symmetry S_nat that generalizes the concept of custodial symmetry, keeping under control deviations from the Standard Model (SM). To realize S_nat linearly, the space of gauge fields has to be extended. Covariant constraints formulated in terms of spurions reduce S_nat back to SU(2)_L x U(1)_Y. This allows for a covariant introduction of explicit S_nat-breaking parameters. We assume that S_nat is at play in a theory of electroweak symmetry-breaking without a light Higgs particle. We describe some consequences of this assumption, using a non-decoupling effective theory in which the loop expansion procedure is based on both momentum and spurion power cou…
An exploratory lattice study of decays at next-to-leading order in the chiral expansion
2005
Abstract We present the first direct evaluation of Δ I = 3 / 2 K → π π matrix elements with the aim of determining all the low-energy constants at NLO in the chiral expansion. Our numerical investigation demonstrates that it is indeed possible to determine the K → π π matrix elements directly for the masses and momenta used in the simulation with good precision. In this range however, we find that the matrix elements do not satisfy the predictions of NLO chiral perturbation theory. For the chiral extrapolation we therefore use a hybrid procedure which combines the observed polynomial behavior in masses and momenta of our lattice results, with NLO chiral perturbation theory at lower masses. …
Phenomenology of dark matter from A(4) flavor symmetry
2011
We investigate a model in which Dark Matter is stabilized by means of a Z2 parity that results from the same non-abelian discrete flavor symmetry which accounts for the observed pattern of neutrino mixing. In our A4 example the standard model is extended by three extra Higgs doublets and the Z2 parity emerges as a remnant of the spontaneous breaking of A4 after electroweak symmetry breaking. We perform an analysis of the parameter space of the model consistent with electroweak precision tests, collider searches and perturbativity. We determine the regions compatible with the observed relic dark matter density and we present prospects for detection in direct as well as indirect Dark Matter s…
Naturality, unification and dark matter
2010
We consider a model where electroweak symmetry breaking is driven by technicolor dynamics with minimal particle content required for walking coupling and saturation of global anomalies. Furthermore, the model features three additional Weyl fermions singlet under technicolor interactions, two of which provide for a one-loop unification of the standard model gauge couplings. Among these extra matter fields exists a possible candidate for weakly interacting dark matter. We evaluate the relic densities and find that they are sufficient to explain the cosmological observations and avoid the experimental limits from earth-based searches. Hence, we establish a nonsupersymmetric framework where hie…
Neutral heavy lepton signatures at the Z0 peak
1990
Abstract Gauge singlet Neutral Heavy Leptons (NHL) arise in many extensions of the standard electroweak theory such as superstring inspired models and their existence may be related to the observed smallness of the neutrino masses. Existing limits on such particles are still fairly poor. A brief discussion is given of the signatures arising from their production through Z 0 → N + ν or Z 0 → N + ν and their subsequent decays within different models. Taking into account the expected luminosities and typical detector efficiencies of the different LEP/SLC experiments one concludes that these may either discover isosinglets or else substantially improve and extend present limits on their mass an…
Electroweak effective theory and beyond Standard Model resonances
2021
We consider a non-linear realization of the electroweak symmetry-breaking pattern $SU(2)_L\times SU(2)_R/SU(2)_{L+R}$ to construct a low-energy effective theory, later extended by the inclusion of heavy new-physics resonances. After assuming appropriate high-energy constraints given by Weinberg sum-rules and the asymptotic behaviour of form-factors, we obtain relations between resonance masses and some low-energy effective couplings. These predictions are compared with current experimental data and some resonance mass bounds are inferred.