arXiv subjects

Jose A. Oller

Publications and source records attributed to Jose A. Oller.

14 recordsLinked to original sources

arXiv2007

Non-Perturbative Study of the Light Pseudoscalar Masses in Chiral Dynamics

We perform a non-perturbative chiral study of the masses of the lightest pseudoscalar mesons. In the calculation of the self-energies we employ the S-wave meson-meson amplitudes taken from Unitary Chiral Perturbation Theory (UCHPT) that include the lightest nonet of scalar resonances. Values for the bare masses of pions and kaons are obtained, as well as an estimate of the mass of the η_8. The former are found to dominate the physical pseudoscalar masses. We then match to the self-energies from Chiral Perturbation Theory (CHPT) to O(p^4), and a robust relation between several O(p^4) CHPT counterterms is obtained. We also resum higher orders from our calculated self-energies. By taking into account values determined from previous chiral phenomenological studies of m_s/\hat{m} and 3L_7+L^r_8, we determine a tighter region of favoured values for the O(p^4) CHPT counterterms 2L^r_6-L^r_4 and 2L^r_8-L^r_5. This determination perfectly overlaps with the recent determinations to O(p^6) in CHPT. We warn about a likely reduction in the value of m_s/\hat{m} by higher loop diagrams and that this is not systematically accounted for by present lattice extrapolations. We also provide a favoured interval of values for m_s/\hat{m} and 3L_7+L^r_8.

hep-ph↗

arXiv2007

S-wave meson scattering up to sqrt{s} < 2 GeV from chiral Lagrangians

The problem of scalar mesons still remains a challenging puzzle, for which we do not even know which are the right pieces to set up. The proliferation of resonances (some of them are very broad and appear on top of hadronic thresholds) and of coupled channels that interact strongly among each other makes the study of this sector a hard task. Our objective is the study of the strongly interacting mesons in coupled channels with quantum numbers J^{PC} = 0^{++} and I=0 and I=1/2, up to a center of mass energy sqrt{s} < 2 GeV. Our framework is based on Unitary Chiral Perturbation Theory. We include for I=0 the channels: ππ, K\bar{K}, ηη, σσ, ηη', ρρ, ωω, η'η', ωϕ, ϕϕ, K^\ast \bar{K}^\ast, a_1(1260)πand π^{\star}(1300)π. In addition, and in order to constrain our fits, we also study the I=1/2, 3/2 channels given by Kπ, Kηand Kη'. We finally present the resonant content of our fits with the $σ$, $f_0(980)$, $f_0(1310)$, $f_(1500)$, $f_0(1710)$ and $f_0(1790)$.

hep-ph↗

arXiv2007

Improved dispersion relations for γγ\to π^0π^0

We perform a dispersive theoretical study of the reaction γγ\to pi^0π^0 emphasizing the low energy region. The large source of theoretical uncertainty to calculate the γγ\toπ^0π^0 total cross section for \sqrt{s}\gtrsim 0.5 GeV within the dispersive approach is removed. This is accomplished by taking one more subtraction in the dispersion relations, where the extra subtraction constant is fixed by considering new low energy constraints, one of them further refined by taking into consideration the f_0(980) region. This allows us to make sharper predictions for the cross section for \sqrt{s}\lesssim 0.8 GeV, below the onset of D-wave contributions. In this way, were new more precise data on γγ\toπ^0π^0 available one might then distinguish between different parameterizations of the ππisoscalar S-wave. We also elaborate on the width of the σresonance to γγand provide new values.

hep-ph↗

arXiv2007

Scalar radius of the pion and zeros in the form factor

The quadratic pion scalar radius, \la r^2\ra^π_s, plays an important role for present precise determinations of ππscattering. Recently, Ynduráin, using an Omnès representation of the null isospin(I) non-strange pion scalar form factor, obtains \la r^2\ra^π_s=0.75\pm 0.07 fm^2. This value is larger than the one calculated by solving the corresponding Muskhelishvili-Omnès equations, \la r^2\ra^π_s=0.61\pm 0.04 fm^2. A large discrepancy between both values, given the precision, then results. We reanalyze Ynduráin's method and show that by imposing continuity of the resulting pion scalar form factor under tiny changes in the input ππphase shifts, a zero in the form factor for some S-wave I=0 T-matrices is then required. Once this is accounted for, the resulting value is \la r^2\ra_s^π=0.65\pm 0.05 fm^2. The main source of error in our determination is present experimental uncertainties in low energy S-wave I=0 ππphase shifts. Another important contribution to our error is the not yet settled asymptotic behaviour of the phase of the scalar form factor from QCD.

hep-ph↗

arXiv2007

Aspects of Strangeness -1 Meson-Baryon Scattering

We consider meson-baryon interactions in S-wave with strangeness -1. This is a sector populated by plenty of resonances interacting in several two-body coupled channels. We consider a large set of experimental data, where the recent experiments are remarkably accurate. This requires a sound theoretical description to account for all the data and we employ Unitary Chiral Perturbation Theory up to and including O(p^2). The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of two Λ(1405) resonances and of the Λ(1670), Λ(1800), Σ(1480), Σ(1620) and Σ(1750). We finally argue about our preferred fit.

hep-ph↗

arXiv2006

On the Strangeness -1 S-wave Meson-Baryon Scattering

We consider meson-baryon interactions in S-wave with strangeness -1. This is a non-perturbative sector populated by plenty of resonances interacting in several two-body coupled channels.We study this sector combining a large set of experimental data. The recent experiments are remarkably accurate demanding a sound theoretical description to account for all the data. We employ unitary chiral perturbation theory up to and including \cal{O}(p^2) to accomplish this aim. The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of the two Λ(1405) resonances and of the Λ(1670), Λ(1800), Σ(1480), Σ(1620) and Σ(1750). We finally argue about our preferred solution.

hep-ph↗

arXiv2006

Reply to Comment on "Surprises in threshold antikaon-nucleon physics"

In their Comment, Borasoy et al. [arXiv:hep-ph/0512279], criticize our results [PRL 95 (2005) 172502] that accommodate both scattering data and the new accurate measurement by DEAR of the shift and width of kaonic hydrogen. In our calculations we have employed unitary chiral perturbation theory (UCHPT). We discuss why their arguments are irrelevant or do not hold.

hep-ph↗

arXiv2005

Surprises in threshold antikaon-nucleon physics

Low energy \bar{K}N interactions are studied within Unitary Chiral Perturbation Theory at next-to-leading order with ten coupled channels. We pay special attention to the recent precise determination of the strong shift and width of the kaonic hydrogen 1s state by the DEAR Collaboration that has challenged our theoretical understanding of this sector of strong interactions. We typically find two classes of solutions, both of them reproducing previous data, that either can or cannot accommodate the DEAR measurements. The former class has not been previously discussed.

hep-ph↗

arXiv2004

Final State Interactions in Hadronic D decays

We show that the large corrections due to final state interactions (FSI) in the D^+\to π^-π^+π^+, D^+_s\to π^-π^+π^+, and D^+\to K^-π^+π^+ decays can be accounted for by invoking scattering amplitudes in agreement with those derived from phase shifts studies. In this way, broad/overlapping resonances in S-waves are properly treated and the phase motions of the transition amplitudes are driven by the corresponding scattering matrix elements determined in many other experiments. This is an important step forward in resolving the puzzle of the FSI in these decays. We also discuss why the σand κresonances, hardly visible in scattering experiments, are much more prominent and clearly visible in these decays without destroying the agreement with the experimental ππand Kπlow energy S-wave phase shifts.

hep-ph↗

arXiv2003

On the resonant and non-resonant contributions to B\toρπ

We discuss the importance of the background in order to understand the scattering in the J^{PC}=0^{++} low and intermediate energy region and in particular regarding the σmeson. In order to appreciate better its importance we compare with the ρmeson in the P-wave ππscattering. We also point out that in present analyses of three-body heavy meson decays, like those of D^+ and B, the role of this background is still not properly settled although it happens to be considerably smaller.

hep-ph↗

arXiv2003

The Mixing Angle of the Lightest Scalar Nonet

We show that the κ, a_0(980), σand the f_0(980) resonances constitute the lightest scalar nonet in three different and complementary ways. First, by establishing the continuous movement of the poles from the physical to a SU(3) limit. Second, by performing an analysis of the couplings of the scalar mesons to pairs of pseudoscalars and third, by analysing the couplings of the scalars with meson-meson SU(3) scattering eigenstates. Every of the last two methods agree that the mixing angle between the singlet and the octet I=0 states is θ= 19^o\pm 5 degrees, so that the σis mainly the singlet and the f_0(980) the isosinglet octet state.

hep-ph↗

arXiv2003

Nucleon-Nucleon Interactions from Effective Field Theory

We have established a new convergent scheme to treat analytically nucleon-nucleon interactions from a chiral effective field theory. The Kaplan-Savage-Wise (KSW) amplitudes are resummed to fulfill the unitarity or right hand cut to all orders below pion production threshold. This is achieved by matching order by order in the KSW power counting the general expression of a partial wave with resummed unitarity cut, with the inverses of the KSW amplitudes. As a result, a new convergent and systematic KSW expansion is derived for an on-shell interacting kernel \cR in terms of which the partial waves are computed. The agreement with data for the S-waves is fairly good up to laboratory energies around 350 MeV and clearly improves and reestablishes the phenomenological success of the KSW amplitudes when treated within this scheme.

nucl-th↗

arXiv2002

Finite width effects in ϕradiative decays

The decay widths ϕ\to γf_0(980) and ϕ\to γa_0(980) are calculated taking into account the finite widths of the scalar resonances f_0(980) and a_0(980). The latter are shown to be essential in order to obtain meaningful results. Simultaneously we also study the decays ϕ\to γπ^0π^0 and γπ^0ηwhere a good reproduction of the recent experimental data is obtained, pointing out the necessity of a ϕγK^0\bar{K}^0 contact vertex. The calculated decay rates to γf_0(980) and γa_0(980) are in good agreement with the experimental ones without invoking isospin breaking in the couplings of the f_0(980) and a_0(980) resonances to the K^+ K^- and K^0 \bar{K}^0 channels, at odds with recent proposals. The derived formula for calculating these ϕradiative decay widths can be also applied in their own experimental analyses in order to obtain more precise results.

hep-ph↗

arXiv2001

Chiral Lagrangians at finite density

The effective SU(2) chiral Lagrangian with external sources is given in the presence of non-vanishing nucleon densities by calculating the in-medium contributions of the chiral pion-nucleon Lagrangian. As a by product, a relativistic quantum field theory for Fermi many-particle systems at zero temperature is directly derived from relativistic quantum field theory with functional methods.

hep-ph↗