arXiv subjects

A. Dobado

Publications and source records attributed to A. Dobado.

67 records · Page 4Linked to original sources

arXiv1996

Higgs Physics in the Large N limit

In this paper we study the large N limit of the Standard Model Higgs sector with $Nλ$, $Ng^2$ and $Ng'^2$ constant and $N$ being the number of would-be Goldstone bosons. Despite the simplicity of this method at leading order, its results satisfy simultaneously important requirements such as unitarity and the low-energy theorems in contrast with other more conventional approaches. Moreover, it is fully compatible with the Equivalence Theorem and it yields a consistent description of the Higgs boson mass and width. Finally we have also included a phenomenological discussion concerning the applications of this method to the LHC.

hep-ph↗

arXiv1995

A note on the GG-->PI 0 PI 0 reaction in the 1/N expansion of ChPT

In this work we present the results of a complete calculation of the $γ γ\rightarrow π^0π^0$ amplitude to leading order in the large $N$ approximation ($N$ being the number of Goldstone bosons) up to order $m^2_π/F^2$. The amplitude turns to be proportional to that of $π^+π^-\rightarrow π^0π^0$. In spite of the fact that this factorization property cannot hold in general (as it was recently pointed out by Morgan and Penington), it appears here since in the large $N$ limit only the $I=J=0$ channel contributes to the $γγ\rightarrow π^0π^0$ reaction. Moreover it seems to be a reasonable approximation in this case since it is possible to reproduce, as a prediction, the experimental data starting from a one-parameter fit of the $ππ$ scattering data.

hep-ph↗

arXiv1995

Learning about the strongly interacting symmetry breaking sector at LHC

In the present work we study the predictions for $WZ$ and $ZZ$ production at LHC with the Electroweak Chiral Lagrangian (EChL) approach. Our analysis will be focused on the less favored case from the experimental point of view, in which the predictions for the gauge bosons scattering amplitudes are considered in the low energy range where, by construction of the low energy approach, they reveal no resonant behavior. The study includes the complete set of amplitudes for all the polarization states of the initial and/or final gauge bosons and makes no use of the Equivalence Theorem. We express the results in terms of the range of values of the chiral parameters that will be accessible at LHC.

hep-ph↗

arXiv1995

DETERMINATION OF THE ELECTROWEAK CHIRAL-LAGRANGIAN PARAMETERS AT THE LHC

In this work we report on the results obtained in a detailed and systematical study of the possibility to measure the parameters appearing in the electroweak chiral lagrangian. The main novelty of our approach is that we do not use the Equivalence Theorem and therefore we work explicitly with all the gauge boson degrees of freedom.

hep-ph↗

arXiv1994

The Applicability of the Equivalence Theorem in $χPT$

We have explicitely calculated the tree level elastic scattering cross sections of two longitudinal gauge bosons, up to four derivatives in the chiral expansion both with and without using the Equivalence Theorem (ET). The numerical results show the existence of new and severe restrictions in the ET energy applicability range, as it was stated in our recent derivation, which we also review here, of the precise ET version in the Chiral Lagrangian description of the Standard Model Symmetry Breaking Sector.

hep-ph↗

arXiv1994

On the Equivalence Theorem in the $χPT$ Description of the Symmetry Breaking Sector of the Standard Model

We develop an alternative formulation of the symmetry breaking sector of the Standard Model as a gauged non-linear sigma model (NLSM) following the philosophy of the Chiral lagrangian approach, which is the only compatible with all the experimental and theoretical constraints. We derive the BRS symmetry of the model and the corresponding quantum lagrangian, which is a generalization of the standard Faddeev-Popov method, in a way which is covariant with respect to the reparametrizations of the coset space of the NLSM. Then we use the BRS invariance of the quantum lagrangian to state the Equivalence Theorem for the renormalized $S$-matrix elements calculated as a chiral expansion.

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arXiv1994

Pion Mass Effects in the Large $N$ Limit of $\chiPT$

We compute the large $N$ effective action of the $O(N+1)/O(N)$ non-linear sigma model including the effect of the pion mass to order $m^2_π/f_π^2$. This action is more complex than the one corresponding to the chiral limit not only because of the pion propagators but also because chiral symmetry produce new interactions proportional to $m^2_π/f_π^2$. We renormalize the action by including the appropriate counter terms and find the renormalization group equations for the corresponding couplings. Then we estudy the unitarity propierties of the scattering amplitudes. Finally our results are applied to the particular case of the linear sigma model and also are used to fit the pion scattering phase shifts.

hep-ph↗

arXiv1994

Inflatonless inflation

Whichever could be the real theory of gravitation, the corresponding low-energy effective lagrangian will probably contain higher derivative terms. In this work we study the general conditions on those terms in order to produce enough inflation to solve some of the problems of the standard Friedmann-Robertson-Walker cosmology in absence of any inflaton field. We apply our results to some particular scenarios where higher derivative terms appear in the effective lagrangian for gravity like those coming from graviton (two)-loops or integrating out ordinary matter (like the one present in the Standard Model).

hep-ph↗

arXiv1994

The Equivalence Theorem for Chiral Lagrangians

In this work we derive the version of the Equivalence Theorem that applies when the symmetry breaking sector of the Standard Model is described by a general chiral lagrangian. The demonstration is valid for renormalized fields for any value of the gauge parameter (in $R_ξ$ gauges) and any parametrization of the coset space. It is based in the absence of gauge anomalies which makes it possible to build an (anti)-BRS invariant chiral lagrangian in terms of the renormalized fields and therefore to use the corresponding Ward identities to obtain the theorem.

hep-ph↗

arXiv1994

One loop calculations on the Wess-Zumino-Witten anomalous functional at finite temperature

We analyze the finite temperature (T) extension of the Wess-Zumino- Witten functional, discussed in a previous work, to one loop in chiral perturbation theory. As a phenomenological application, we calculate finite temperature corrections to the amplitude of the $π^0$ decay into two photons. This calculation is performed in three limits : i)$T/M_π<<1$, ii)the chiral limit at finite T and iii)$T/M_π>>1$ ($M_π$ being the pion mass). The $T$-corrections tend to vanish in the chiral limit, where only the kaon contribution remains (although it is exponentially suppressed).

hep-ph↗

arXiv1993

On the Wess-Zumino-Witten anomalous functional at finite temperature

We discuss the finite temperature extension of the anomalous Wess-Zumino -Witten lagrangian. The finite temperature S^1\times S^3 compactification makes a structure in disconnected sectors, corresponding to different baryon numbers appear naturally. The consistency of the anomalous functional is proved for arbitrary baryon number configurations. The anomalous behavior of the functional is shown to be consistent with the absence of finite temperature corrections to chiral anomalies in QCD, for each baryon number sector.

hep-ph↗

arXiv1993

Some consequences of the effective low-energy lagrangian for gravity

We consider the minimal low-energy action for gravity up to six derivatives which is renormalizable at the two-loop level modulo higher derivative corrections. Then we study the classical solutions corresponding to the Schwarzschild and the Robertson-Walker metrics. In the first case we find a singularity close to the gravitational radius and in the second case we find inflationary de Sitter solutions in absence of any matter or cosmological constant.

hep-ph↗

arXiv1993

A global fit of $ππ$ and $πK$ elastic scattering in ChPT with dispersion relations

We apply the one-loop results of the $SU(3)_L\times SU(3)_R$ ChPT suplemented with the inverse amplitude method to fit the available experimental data on $ππ$ and $πK$ scattering. With esentially only three parameters we describe accurately data corresponding to six different channels, namely $(I,J)=(0,0), (2,0), (1,1), (1/2,0), (3/2,0)$ and $(1/2,1)$. In addition we reproduce the first resonances of the $(1,1)$ and $(1/2,1)$ channel with the right mass corresponding to the $ρ$ and the $K^*(892)$ particles.

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