arXiv subjects
Publications and source records attributed to R. Escribano.
A phenomenological analysis of various decay processes is performed in order to test the large $N_c$ Chiral Perturbation Theory predictions for the octet and singlet pseudoscalar decay constants and mixing angles. The results obtained hint at a disagreement with the expectations of this theoretical framework although the statistical significance is still limited.
An analysis of various radiative $VPγ$ decays is performed using the two mixing angle description of the $η$-$η^\prime$ system. The agreement is excellent. Our results are expressed both in the ``octet-singlet'' and in the ``quark-flavour'' basis. It turns out that at the present experimental accuracy, the two angles are significantly different in the former, but not in the latter basis.
A test on quantum mechanics proposed long ago by Karl Popper is reconsidered with further detail and new insight. An ambiguity in the proposal, which turns out to be essential in order to make the test conclusive, is identified and taken into account for the first time. Its implications for recently performed photon experiments [such as in D. V. Strekalov \textit{et al.}, Phys. Rev.\ Lett. {\bf 74}, 3600 (1995)] are briefly analyzed.
An analysis of various decay processes is performed using the two mixing angle description of the $η$-$η^\prime$ system, incorporating the link to the gluonic sector through anomalies. The agreement is excellent. For comparison with previous works, our results are expressed both in the ``octet-singlet'' and in the ``quark-flavour'' basis. It turns out that at the present experimental accuracy, the two angles are significantly different in the former, but not in the latter basis. The implications of our analysis for the Large $N_c$ $χ$PT predictions are also discussed.
A test of quantum mechanics proposed by K. Popper and dealing with two-particle entangled states emitted from a fixed source has been criticized by several authors. Some of them claim that the test becomes inconclusive once all the quantum aspects of the source are considered. Moreover, another criticism states that the predictions attributed to quantum mechanics in Popper's analysis are untenable. We reconsider these criticisms and show that, to a large extend, the `falsifiability' potential of the test remains unaffected.
Recent proposals to test Bell's inequalities with entangled pairs of pseudoscalar mesons are reviewed. This includes pairs of neutral kaons or B-mesons and offers some hope to close both the locality and the detection loopholes. Specific difficulties, however, appear thus invalidating most of those proposals. The best option requires the use of kaon regeneration effects and could lead to a successful test if moderate kaon detection efficiencies are achieved.
We analyse the recent claim that a violation of a Bell's inequality has been observed in the $B$--meson system [A. Go, {\em Journal of Modern Optics} {\bf 51} (2004) 991]. The results of this experiment are a convincing proof of quantum entanglement in $B$--meson pairs similar to that shown by polarization entangled photon pairs. However, we conclude that the tested inequality is not a genuine Bell's inequality and thus cannot discriminate between quantum mechanics and local realistic approaches.
A consistent description of $σ(500)$ meson effects in $ρ^0\toπ^0π^0γ$ and $π^+π^-γ$ decays is proposed in terms of reasonably simple amplitudes which reproduce the expected chiral-loop behaviour for large $m_σ$ values. For the neutral case, in addition to the well known $ω$ exchange, there is an important contribution from the $σ(500)$ meson that is in agreement with recent experimental data. For the charged case, where the dominant contribution comes from bremsstrahlung, the effects of the $σ(500)$ meson are relevant only at high values of the photon energy and compatible with present data. A combined analysis of both processes with moderately improved experimental information should contribute decisively to clarify the status of this controversial $σ(500)$ meson.
A comparison of the linear sigma model (L$σ$M) and Chiral Perturbation Theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and next-to-leading order terms in the ChPT amplitudes are reproduced if one restricts to scalar resonance exchange. Some low energy constants of the order $p^4$ ChPT Lagrangian are fixed in terms of scalar meson masses. Present values of these low energy constants are compatible with the L$σ$M dynamics. We conclude that more accurate values would be most useful either to falsify the L$σ$M or to show its capability to shed some light on the controversial scalar physics.
Using the pole approach we determine the mass and width of the $f_0(980)$; in particular, we analyze the possibility that two nearby poles are associated to it. We restrict our analysis to a neighborhood of the resonance, using $ππ$ data for the phase shift and inelasticity, and the invariant mass spectrum of the $J/ψ\toϕππ, ϕK\bar K$ decays. The formalism we use is based on unitarity and a generalized version of the Breit-Wigner parameterization. We find that a single pole describes the $f_0(980)$, the precise position depending upon the $ππ$ data used. As a byproduct, values for the $g_{f_0ππ}$ and $g_{f_0K\bar K}$ coupling constants are obtained.
The complementarity between Chiral Perturbation Theory and the Linear Sigma Model is exploited to study $π^0π^0$ production in $ϕ$ radiative decays, where the effects of the $f_0(980)$ scalar resonance, and those of its more controversial $σ(500)$ partner, should become manifest via the $ϕ\to K^+ K^- (γ)\toπ^0π^0γ$ decay chain. The recently reported data on $ϕ\toπ^0π^0γ$ coming from the VEPP-2M $e^+ e^-$ collider in Novosibirsk and the DA$Φ$NE $ϕ$-factory in Frascati can be reasonably described in our approach, which we propose as a promising first step towards more detailed analyses. The $f_0(980)$ contribution, which appears as a moderately narrow peak at the high part of the dipion mass spectrum, can be interpreted as the isoscalar member of the scalar nonet with a large $f_0 K\bar{K}$ coupling and an $f_0ππ$ coupling suppressed by almost ideal $σ$-$f_0$ mixing. Indeed, the mixing angle in the flavour basis is found to be $ϕ_{S}\approx -6^\circ$, if the $f_0$-propagator is approximated by a simple Breit-Wigner, or $ϕ_{S}\approx -9^\circ$, if an improved two-channel analysis is performed. The $σ(500)$ resonance, which is then strongly coupled to pion pairs, yields a tiny contribution because, in our approach, its coupling to kaon pairs is proportional to $m^2_σ-m^2_K$ and thus quite small.
We discuss the gravitational lensing of neutrinos by astrophysical objects. Unlike photons, neutrinos can cross a stellar core; as a result, the lens quality improves. We also estimate the depletion of the neutrino flux after crossing a massive object and the signal amplification expected. While Uranians alone would benefit from this effect in the Sun, similar effects could be considered for binary systems.
The complementarity between Chiral Perturbation Theory and the Linear Sigma Model in the scalar channel is exploited to study $π^0π^0$ production in $ρ$ and $ω$ radiative decays, where the effects of a low mass scalar resonance $σ(500)$ should manifest. The recently reported data on $ρ\toπ^0π^0γ$ seem to require the contribution of a low mass and moderately narrow $σ(500)$. The properties of this controversial state could be fixed by improving the accuracy of these measurements. Data on $ω\toπ^0π^0γ$ can also be accommodated in our framework, but are much less sensitive to the $σ(500)$ properties.
A prediction for the contributions of chiral loops and the L$σ$M model to the radiative $ϕ\toπ^0ηγ$ decay mode is presented. The L$σ$M is used as an appropriate framework for describing the pole effects of the $a_0(980)$ scalar resonance. As a result, a better agreement with present available data is achieved for the higher part of the $π^0η$ invariant mass spectrum. For the branching ratio, a value of $B(ϕ\toπ^0ηγ)=(0.75$--$0.95)\times 10^{-4}$ is found.
A value for the $η$-$η^\prime$ mixing angle is extracted from the data on $VPγ$ transitions using simple quark-model ideas. The set of data covers {\it all} possible radiative transitions between the pseudoscalar and vector meson nonets. Two main ingredients of the model are the introduction of flavour-dependent overlaps for the various $q\bar{q}$ wave functions and the use of the quark-flavour basis to describe the $η$-$η^\prime$ system. In this basis the mixing angle is found to be $ϕ_P=(37.7\pm 2.4)^\circ$.
The radiative $ϕ\toπ^0ηγ$ decay is discussed emphasizing the effects of the $a_0$(980) scalar resonance which dominates the high values of the $π^0η$ invariant mass spectrum. In its lowest part, the proposed amplitude coincides with the reliable and ChPT-inspired contribution coming from chiral loops. The $a_0$(980) resonance is then incorporated exploiting the complementarity between ChPT and the linear sigma model for this channel. The recently reported experimental invariant mass distribution and branching ratio can be satisfactorily accommodated in our framework. For the latter, a value of $B(ϕ\toπ^0ηγ)$ in the range $(0.75$--$0.95)\times 10^{-4}$ is predicted.
The ratio Phi->K+K-/K0K0bar is discussed and its present experimental value is compared with theoretical expectations. A difference larger than two standard deviations is observed. We critically examine a number of mechanisms that could account for this discrepancy, which remains unexplained. Measurements at DAPHNE at the level of the per mille accuracy can clarify whether there exist any anomaly.
We study the temperature dependence of the eta and eta' meson masses within the framework of U(3)_L x U(3)_R chiral perturbation theory, up to next-to-leading order in a simultaneous expansion in momenta, quark masses and number of colours. We find that both masses decrease at low temperatures, but only very slightly. We analyze higher order corrections and argue that large N_c suggests a discontinuous drop of M_eta' at the critical temperature of deconfinement T_c, consistent with a first order transition to a phase with approximate U(1)_A symmetry.