56306636
Light composite Higgs from an effective action for technicolor
We compute an effective action for a composite Higgs boson formed by new fermions belonging to a general technicolor non-Abelian gauge theory, using a quite general expression for the fermionic self-energy that depends on a certain parameter ($\ensuremath{\alpha}$), that defines the technicolor theory from the extreme walking behavior up to the one with a standard operator product expansion behavior. We discuss the values of the trilinear and quadrilinear scalar couplings. Our calculation spans all the possible physical possibilities for mass and couplings of the composite system. In the case of extreme walking technicolor theories we verify that it is possible to have a composite Higgs boson with a mass as light as the present experimental limit, contrary to the usual expectation of a heavy mass for the composite Higgs boson. In this case we obtain an upper limit for the Higgs boson mass, (${M}_{H}\ensuremath{\le}\mathcal{O}(700)\text{ }\text{ }\mathrm{GeV}$ for $SU(2{)}_{\mathrm{TC}}$), and the experimental data on the Higgs boson mass constrain $SU(N{)}_{\mathrm{TC}}$ technicolor gauge groups to be smaller than $SU(10{)}_{\mathrm{TC}}$.
31668493
Relating a gluon mass scale to an infrared fixed point in pure gauge QCD.
We show that in pure gauge QCD (or any pure non-Abelian gauge theory) the condition for the existence of a global minimum of energy with a gluon (gauge boson) mass scale also implies the existence of a fixed point of the beta function. We argue that the frozen value of the coupling constant found in some solutions of the Schwinger-Dyson equations of QCD can be related to this fixed point. We also discuss how the inclusion of fermions modifies this property.
42724469
Discrete symmetries, invisible axion, and lepton number symmetry in an economic 3-3-1 model
We show that Peccei-Quinn and lepton number symmetries can be a natural outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z11^ Z2 symmetry. This symmetry is suitably accommodated in this model when we augment its spectrum by including merely one singlet scalar field. We work out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study the phenomenological consequences. The main result of this work is that the solution to the strong CP problem can be implemented in a natural way, implying an invisible axion phenomenologically unconstrained, free of domain wall formation, and constituting a good candidate for the cold dark matter. DOI: 10.1103/PhysRevD.68.115009
124456081
LIMIT ON A HEAVY DIRAC NEUTRINO THROUGH OBLIQUE RADIATIVE CORRECTIONS
We compute the one-loop oblique corrections in a typical model with neutrino masses due to the seesaw mechanism. We verify that a Dirac neutrino mass up to 178 GeV is still allowed by the experimental data.
7238147
Neutrino decay and neutrinoless double beta decay in a 3-3-1 model
In this work we show that the implementation of spontaneous breaking of the lepton number in the 3-3-1 model with right-handed neutrinos gives rise to fast neutrino decay with Majoron emission and generates a bunch of new contributions to the neutrinoless double beta decay.
118596316
Fitting the lattice gluon propagator and the question of positivity violation
The solution of Alkofer et al for the gluon propagator in Landau gauge of the Dyson‐Schwinger equations was fitted with several functional forms. We study if the lattice gluon propagator, computed using large asymmetric lattices, is well reproduced by such functional forms. Furthermore, we also check for the violation of positivity of the lattice gluon propagator.
18513841
Fitting BOOMERANG and MAXIMA-1 data with a Einstein–Yang–Mills cosmological model
Abstract We analyse the implications of recent Cosmic Microwave Background (CMB) data for a specific cosmological model, based on the higher-dimensional Einstein–Yang–Mills system compactified on a R × S 3 × S d topology and conclude that the model parameters are tightly constrained by CMB spectra. Moreover, the model predicts a relationship between the deceleration parameter at present, q 0 , and some characteristic features of CMB spectra, namely, the height of the first peak and the the location of the second peak, that is consistent with the observations and which can be further tested by future CMB and other experiments.
59494185
What Lattice QCD tell us about the Landau Gauge Infrared Propagators
The calculation of the Landau gauge gluon propagator performed in Coimbra using lattice QCD simulations is reviewed. Particular attention is given to t he behavior of the gluon propagator in the infrared region and the value of D(0). In the second part of the article, the modeling of the lattic e data using massive type propagators and Gribov type propagators is discussed. Four different mass scales are required to describe the propagator over the full range of momenta accessed by the simulations discussed here. Furthermore, assuming a momentum dependent gluon mass, we sketch on its functional dependence.
118655256
The lattice gluon propagator in Landau gauge at zero and finite temperature
The interplay between the finite volume and finite lattice spacing is investigated using lattice QCD simulations to compute the Landau gauge gluon propagator at zero temperature. Comparing several ensembles with different lattice spacings and physical volumes, we conclude that the dominant effects, in the infrared region, are associated with the use of a finite lattice spacing. The simulations show that decreasing the lattice spacing, while keeping the same physical volume, leads to an enhancement of the infrared gluon propagator. Moreover, we also present results for the Landau gauge gluon propagator at finite temperature.
209836416
Evidence for the direct decay of the 125 GeV Higgs boson to fermions
The discovery of a new boson with a mass of approximately 125 GeV in 2012 at the Large Hadron Collider1, 2, 3 has heralded a new era in understanding the nature of electroweak symmetry breaking and possibly completing the standard model of particle physics4, 5, 6, 7, 8, 9. Since the first observation in decays to γγ, WW and ZZ boson pairs, an extensive set of measurements of the mass10, 11 and couplings to W and Z bosons11, 12, 13, as well as multiple tests of the spin-parity quantum numbers10, 11, 13, 14, have revealed that the properties of the new boson are consistent with those of the long-sought agent responsible for electroweak symmetry breaking. An important open question is whether the new particle also couples to fermions, and in particular to down-type fermions, as the current measurements mainly constrain the couplings to the up-type top quark. Determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays, as recently reported by the Compact Muon Solenoid (CMS) experiment in the study of Higgs decays to bottom quarks15 and τ leptons16. Here, we report the combination of these two channels, which results in strong evidence for the direct coupling of the 125 GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected.