arXiv subjects

J. A. Oller

Publications and source records attributed to J. A. Oller.

At least 91 records · Page 5Linked to original sources

arXiv2010

The phi(1020) a0(980) S-wave scattering and hints for a new vector-isovector resonance

We have studied the phi(1020)a0(980) S-wave scattering at threshold energies employing chiral Lagrangians coupled to vector mesons by minimal coupling. The interaction is described without new free parameters by considering the scalar isovector a0(980) resonance as dynamically generated in coupled channels, and demanding that the recently measured e+ e- -> phi(1020) f0(980) cross section is reproduced. For some realistic choices of the parameters, the presence of a dynamically generated isovector companion of the Y(2175) is revealed. We have also investigated the corrections to the e+ e- -> phi(1020) pi0 eta reaction cross section that arise from phi(1020)a0(980) re-scattering in the final state. They are typically large and modify substantially the cross section. For a suitable choice of parameters, the presence of the resonance would manifest itself as a clear peak at sqrt{s}~2.03 GeV in e+ e- -> phi(1020) pi0 eta.

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arXiv2010

The chiral quark condensate and pion decay constant in nuclear matter at next-to-leading order

Making use of the recently developed chiral power counting for the physics of nuclear matter [1,2], we evaluate the in-medium chiral quark condensate up to next-to-leading order for both symmetric nuclear matter and neutron matter. Our calculation includes the full in-medium iteration of the leading order local and one-pion exchange nucleon-nucleon interactions. Interestingly, we find a cancellation between the contributions stemming from the quark mass dependence of the nucleon mass appearing in the in-medium nucleon-nucleon interactions. Only the contributions originating from the explicit quark mass dependence of the pion mass survive. This cancellation is the reason of previous observations concerning the dominant role of the long-range pion contributions and the suppression of short-range nucleon-nucleon interactions. We find that the linear density contribution to the in-medium chiral quark condensate is only slightly modified for pure neutron matter by the nucleon-nucleon interactions. For symmetric nuclear matter the in-medium corrections are larger, although smaller compared to other approaches due to the full iteration of the lowest order nucleon-nucleon tree-level amplitudes. Our calculation satisfies the Hellmann-Feynman theorem to the order worked out. Also we address the problem of calculating the leading in-medium corrections to the pion decay constant. We find that there are no extra in-medium corrections that violate the Gell-Mann-Oakes-Renner relation up to next-to-leading order.

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arXiv2010

Non-perturbative methods for a chiral effective field theory of finite density nuclear systems

Recently we have developed a novel chiral power counting scheme for an effective field theory of nuclear matter with nucleons and pions as degrees of freedom [1]. It allows for a systematic expansion taking into account both local as well as pion-mediated multi-nucleon interactions. We apply this power counting in the present study to the evaluation of the pion self-energy and the energy density in nuclear and neutron matter at next-to-leading order. To implement this power counting in actual calculations we develop here a non-perturbative method based on Unitary Chiral Perturbation Theory for performing the required resummations. We show explicitly that the contributions to the pion self-energy with in-medium nucleon-nucleon interactions to this order cancel. The main trends for the energy density of symmetric nuclear and neutron matter are already reproduced at next-to-leading order. In addition, an accurate description of the neutron matter equation of state, as compared with sophisticated many-body calculations, is obtained by varying only slightly a subtraction constant around its expected value. The case of symmetric nuclear matter requires the introduction of an additional fine-tuned subtraction constant, parameterizing the effects from higher order contributions. With that, the empirical saturation point and the nuclear matter incompressiblity are well reproduced while the energy per nucleon as a function of density closely agrees with sophisticated calculations in the literature.

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arXiv2009

Chiral Effective Field Theory for Nuclear Matter with long- and short-range Multi-Nucleon Interactions

We derive a novel chiral power counting scheme for in-medium chiral perturbation theory with explicit nucleonic and pionic degrees of freedom coupled to external sources. It allows for a systematic expansion taking into account local as well as pion-mediated inter-nucleon interactions. Based on this power counting, one can identify classes of non-perturbative diagrams that require a resummation. Within this scheme, the pion self-energy in asymmetric nuclear matter is analyzed and calculated up-to-and-including next-to-leading order (NLO). It is shown that the corrections involving in-medium nucleon-nucleon interactions cancel between each other at NLO. As a result, there are no corrections up to this order to the linear density approximation for the in-medium pion self-energy.

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arXiv2009

On the ϕ(1020)f_0(980) S-wave scattering and the Y(2175) resonance

We have studied the ϕ(1020)f_0(980) S-wave scattering at energies around threshold employing chiral Lagrangians coupled to vector mesons through minimal coupling. The interaction kernel is obtained by considering the f_0(980) as a K\bar{K} bound state. The Y(2175) resonance is generated in this approach by the self-interactions between the ϕ(1020) and the f_0(980) resonances. We are able to describe the e^+e^-\to ϕ(1020)f_0(980) recent scattering data to test experimentally our scattering amplitudes, concluding that the Y(2175) resonance has a large ϕ(1020)f_0(980) meson-meson component.

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arXiv2008

Chiral Unitary Dynamics of Hadrons and Hadrons in a Nuclear Medium

In this talk I summarize recent findings around the description of axial vector mesons as dynamically generated states from the interaction of pseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states, and how some recent experiment supports the existence of the new hidden charm scalar state predicted. I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels. Then show the differences with the S=0 case, where the $N^*(1710)$ appears also dynamically generated from the two pion one nucleon system, but the $N^*(1440)$ does not appear, indicating a more complex structure of the Roper resonance. Finally I shall show how the state X(2175), recently discovered at BABAR and BES, appears naturally as a resonance of the $ϕK \bar{K}$ system.

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arXiv2008

S-wave γγ\to ππand f_0(980)\to ππ

We report on a dispersion relation for the γγ\to (ππ)_I S-wave in isospin I emphasizing the low energy region. The f_0(980) signal that emerges in γγ\to ππis also discussed. Our results could be used to distinguish between different ππisoscalar S-wave parameterizations. We also calculate the width of the σresonance to γγand obtain the value Γ(σ\toγγ)=(1.68\pm 0.15) KeV. Finally, we elaborate on the size of the f_0(980) coupling to ππand show that its smallness compared to the K\bar{K} one is not related to the OZI rule.

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arXiv2008

S-wave meson scattering up to 2 GeV and its spectroscopy

We have performed a thorough study of the meson-meson S-waves with isospin (I) 0 and 1/2, up to sqrt(s) ~ 2 GeV. This is the first study that includes 13 channels that have their threshold below that energy. All the resonances below 2 GeV, namely the f_0(600) or sigma, f_0(980), f_0(1370), f_0(1500), f_0(1710) and f_0(1790) for I=0, and the K*_0(800) or kappa, K*_0(1430) and K*_0(1950) for I=1/2, are generated. We can then extract a clear picture of the spectroscopy, finding that the f_0(1710), together with an important contribution to the f_0(1500), are glueballs. Another pole, which corresponds mainly to the f_0(1370), is a pure octet I=0 state, and does not mix with the glueball.

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arXiv2008

Identification of a Scalar Glueball

We have performed a coupled channel study of the meson-meson S-waves involving isospins (I) 0, 1/2 and 3/2 up to 2 GeV. For the first time the channels ππ, K\bar{K}, ηη, σσ, ηη', η'η', ρρ, ωω, ωϕ$, ϕϕ, a_1πand π^*πare considered. All the resonances with masses below 2 GeV for I=0 and 1/2 are generated by the approach. We identify the f_0(1710) and a pole at 1.6 GeV, which is an important contribution to the f_0(1500), as glueballs. This is based on an accurate agreement of our results with predictions of lattice QCD and the chiral suppression of the coupling of a scalar glueball to \bar{q}q. Another nearby pole, mainly corresponding to the f_0(1370), is a pure octet state not mixed with the glueball.

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arXiv2008

Two photons into π^0π^0

We perform a theoretical study based on dispersion relations of the reaction γγ\to π^0π^0 emphasizing the low energy region. We discuss how the f_0(980) signal emerges in γγ\to ππwithin the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ\to ππamplitude above the K\bar{K} threshold. This allows us to make sharper predictions for the cross section at lower energies and our results could then be used to distinguish between different ππisoscalar S-wave parameterizations with the advent of new precise data on γγ\toπ^0π^0. We compare our dispersive approach with an updated calculation employing Unitary Chiral Perturbation Theory (U\chiPT). We also pay special attention to the role played by the σresonance in γγ\toππand calculate its coupling and width to gammaγ, for which we obtain Γ(σ\toγγ)=(1.68\pm 0.15) KeV.

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arXiv2007

Recent Developments in Chiral Unitary Dynamics of Resonances

In this talk I summarize recent findings made on the description of axial vector mesons as dynamically generated states from the interaction of peseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states. Finally, I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels dynamics.

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arXiv2007

The WA3 data and the two $K_1(1270)$ resonances

Recent studies based on unitary chiral perturbation theory (U$χ$PT) found that the low-lying axial vector mesons can be dynamically generated due to the interaction of the pseudoscalar octet of the pion and the vector nonet of the rho. In particular, two poles in the second Riemann sheet have been associated to the nominal $K_1(1270)$ resonance. In this talk, we present a recent analysis of the WA3 data on $K^-p\to K^-π^+π^- p$ at 63 GeV using the U$χ$PT amplitudes, and show that it is in favor of the existence of two $K_1(1270)$'s [Phys. Rev. D 75, 014017 (2007)].

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arXiv2007

Scalar radius of the pion and two photons into two pions. Strong S-wave final state interactions

The quadratic pion scalar radius, ^π_s, plays an important role for present precise determinations of ππscattering. The solution of the Muskhelishvili-Omnès equations for the non-strange null isospin (I) pion scalar form factor determines that ^π_s=(0.61\pm 0.04) fm^2. However, by using an Omnès representation of this form factor, Ynduráin recently obtains ^π_s=(0.75\pm 0.07) fm^2. A large discrepancy between both values, given the precision, then results. We show that Ynduráin's method is indeed compatible with the determinations from the Muskhelishvili-Omnès equations once a zero in the scalar form factor for some S-wave I=0 T-matrices is considered. Once this is accounted for, the resulting value is ^π=(0.63\pm 0.05) fm^2. On the other hand, we perform a theoretical study of the reaction γγ\to π^0π^0 based on dispersion relations. The large source of uncertainty for \sqrt{s}\gtrsim 0.5 GeV, due to variations in the phase used in the Omnès function above the K\bar{K} threshold, is removed by taking one more subtraction in the dispersion relation. This allows us to make sharper predictions for the cross section so that one could use this reaction to distinguish between different low energy ππparameterizations, once independent experiments are available. We also study the role played by the σor f_0(600) meson in this reaction and determine its width to two photons.

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arXiv2007

Clues for the existence of two $K_1(1270)$ resonances

The axial vector meson $K_1(1270)$ was studied within the chiral unitary approach, where it was shown that it has a two-pole structure. We reanalyze the high-statistics WA3 experiment $K^- p\to K^-π^+π^- p$ at 63 GeV, which established the existence of both $K_1(1270)$ and $K_1(1400)$, and we show that it clearly favors our two-pole interpretation. We also reanalyze the traditional K-matrix interpretation of the WA3 data and find that the good fit of the data obtained there comes from large cancellations of terms of unclear physical interpretation.

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arXiv2006

Scalar K pi form factor and light quark masses

Recent experimental improvements on K-decay data allow for a precise extraction of the strangeness-changing scalar K pi form factor and the related strange scalar spectral function. On the basis of this scalar as well as the corresponding pseudoscalar spectral function, the strange quark mass is determined to be m_s(2 GeV) = 92 +- 9 MeV. Further taking into account chiral perturbation theory mass ratios, the light up and down quark masses turn out to be m_u(2 GeV) = 2.7 +- 0.4 MeV as well as m_d(2 GeV) = 4.8 +- 0.5 MeV. As a by-product, we also find a value for the Cabibbo angle |V_{us}| = 0.2236(29) and the ratio of meson decay constants F_K/F_π= 1.203(16). Performing a global average of the strange mass by including extractions from other channels as well as lattice QCD results yields m_s(2 GeV) = 94 +- 6 MeV.

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arXiv2005

Dynamical baryon resonances from chiral unitarity

We report on the latests developments in the field of baryonic resonances generated from the meson-baryon interaction in coupled channels using a chiral unitary approach. The collection of resonances found in different strangeness and isospin sectors can be classified into SU(3) multiplets. The Lambda(1405) emerges as containing the effect of two poles of the scattering amplitude and various reactions that might preferentially select one or the other pole are discussed.

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arXiv2005

Structure of Lambda(1405) and chiral dynamics

We report on a recent theoretical work on the structure of the Lambda(1405) resonance within a chiral unitary approach, in which the resonance is dynamically generated in meson-baryon scattering. Studying the analytic structure of the scattering amplitude, we have found that there are two poles lying around energies of Lambda(1405) with different widths and couplings to the meson-baryon states. We discuss reactions to conform the double pole structure in experiment and elastic K^- p scattering at low energies.

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arXiv2004

Chiral dynamics of the two Lambda(1405) states

The Lambda(1405) resonance is studied by a chiral unitary approach, in which the resonance is dynamically generated in coupled-channel meson-baryon scattering. Investigating the analytic structure of the scattering amplitudes obtained by the chiral unitary approach, we find two poles around the energies of the Lambda(1405) coupling differently to the meson-baryon states. We reach the conclusion that the Lambda(1405) resonance seen in experiments is not just one single resonance, but a superposition of these two states.

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