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E. Ruiz Arriola

Publications and source records attributed to E. Ruiz Arriola.

At least 145 records · Page 8Linked to original sources
arXiv2005

Renormalization of the Deuteron with One Pion Exchange

We analyze the deuteron bound state through the One Pion Exchange Potential. We pay attention to the short distance peculiar singularity structure of the bound state wave functions in coordinate space and the elimination of short distance ambiguities by selecting the regular solution at the origin. We determine the so far elusive amplitude of the converging exponential solutions at the origin. All bound state deuteron properties can then be uniquely deduced from the deuteron binding energy, the pion-nucleon coupling constant and pion mass. This generates correlations among deuteron properties. Scattering phase shifts and low energy parameters in the 3S1-3D1 channel are constructed by requiring orthogonality of the positive energy states to the deuteron bound state, yielding an energy independent combination of boundary conditions. We also analyze from the viewpoint of short distance boundary conditions the weak binding regime on the light of long distance perturbation theory and discuss the approach to the chiral limit.

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arXiv2004

Chiral Lagrangians at finite temperature and the Polyakov Loop

Heat kernel expansions at finite temperature of massless QCD and chiral quark models generate effective actions relevant for both low and high temperature QCD. The key relevance of the Polyakov Loop to maintain the large and non-perturbative gauge invariance at finite temperature is stressed.

hep-ph↗
arXiv2004

Singlet NN Regularization using a Boundary Condition for OPE and TPE potentials

Boundary conditions provide a simple and physically compelling Wilsonian renormalization method in coordinate space in the framework of effective field theory as applied to nucleon-nucleon interaction in the non perturbative regime, enabling to remove unphysical regularization cut-offs while keeping physical low energy threshold parameters such as the scattering length and effective range invariant. We illustrate how the method successfully works in the $^1S_0$ channel for the One Pion Exchange (OPE) and Two Pion Exchange (TPE) potentials

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arXiv2004

Polyakov Loop at Finite Temperature in Chiral Quark Models

At finite temperature, chiral quark models do not incorporate large gauge invariance which implies genuinely non-perturbative finite temperature gluonic degrees of freedom. Motivated by this observation, we describe how the coupling of the Polyakov loop as an independent degree of freedom to quarks not only accounts for large gauge invariance, but also allows to establish in a dynamical way the interaction between composite hadronic states such as Goldstone bosons to finite temperature non-perturbative gluons in a medium which can undergo a confinement-deconfinement phase transition.

hep-ph↗
arXiv2004

Determination of low energy parameters for NN-scattering at $N^4 LO$ in all partial waves with $j\le 5$

The Variable S-matrix approach offers a unique way to extract low energy threshold parameters for a given NN potential. We extract those parameters for the np system from the NijmII and Reid93 potentials, to all partial waves with total angular momentum $j \le m5 $, using the generalized effective range expansion % $$ ({\bf f}^{sj})_{l,l'} k^l k^{l'} = -({{\bf a}^{sj}}^{-1})_{l,l'} + \frac12 ({\bf r}^{sj})_{l,l'} k^2 + ({\bf v_2}^{sj})_{l,l'} k^4 + + ({\bf v_3}^{sj})_{l,l'} k^6 + + ({\bf v_4}^{sj})_{l,l'} k^8 + ... - {\rm i} k^{l+l'+1} $$ % where $ {\bf f}^{sj} = ({\bf S}^{sj} - {\bf 1}) / (2 {\rm i} k) $ is the scattering amplitude and ${\bf S}^{sj}$ is the unitary S-matrix in coupled channel space with total spin $s$ and total angular momentum $j$. Our calculation includes all the relevant contributions of the full amplitude to order ${\cal O} (k^8) $ in the CM momentum. We also discuss the validity of the generalized effective range expansion in the region of analyticity $ k \le m_π/2$.

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arXiv2004

Renormalization of NN-Scattering with One Pion Exchange and Boundary Conditions

A non perturbative renormalization scheme for Nucleon-Nucleon interaction based on boundary conditions at short distances is presented and applied to the One Pion Exchange Potential. It is free of off-shell ambiguities and ultraviolet divergences, provides finite results at any step of the calculation and allows to remove the short distance cut-off in a suitable way. Low energy constants and their non-perturbative evolution can directly be obtained from experimental threshold parameters in a completely unique and model independent way when the long range explicit pion effects are eliminated. This allows to compute scattering phase shifts which are, by construction consistent with the effective range expansion to a given order in the C.M. momentum $p$. In the singlet $^1S_0$ and triplet $^3S_1- ^3D_1$ channels ultraviolet fixed points and limit cycles are obtained respectively for the threshold parameters. Data are described satisfactorily up to CM momenta of about $p \sim m_π$.

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arXiv2004

Low Energy Chiral Lagrangian in Curved Space-Time from the Spectral Quark Model

We analyze the recently proposed Spectral Quark Model in the light of Chiral Perturbation Theory in curved space-time. In particular, we calculate the chiral coefficients $L_1, ..., L_{10}$, as well as the coefficients $L_{11}$, $L_{12}$, and $L_{13}$, appearing when the model is coupled to gravity. The analysis is carried for the SU(3) case. We analyze the pattern of chiral symmetry breaking as well as elaborate on the fulfillment of anomalies. Matching the model results to resonance meson exchange yields the relation between the masses of the scalar, tensor and vector mesons, $M_{f_0}=M_{f_2}=\sqrt{2} M_V= 4 \sqrt{3 /N_c} πf_π$. Finally, the large-$N_c$ limit suggests the dual relations in the vector and scalar channels, $M_V=M_S= 2 \sqrt{6 /N_c} πf_π$ and $ ^{1/2}_S = < r^2 >^{1/2}_V = 2 \sqrt{N_c} / f_π= 0.59 {\rm fm} $.

hep-ph↗
arXiv2003

The thermal heat kernel expansion and the one-loop effective action of QCD at finite temperature

The heat kernel expansion for field theory at finite temperature is constructed. It is based on the imaginary time formalism and applies to generic Klein-Gordon operators in flat space-time. Full gauge invariance is manifest at each order of the expansion and the Polyakov loop plays an important role at any temperature. The expansion is explicitly worked out up to operators of dimension six included. The method is then applied to compute the one loop effective action of QCD at finite temperature with massless quarks. The calculation is carried out within the background field method in the $\bar{\text{MS}}$ scheme up to dimension six operators. Further, the action of the dimensionally reduced effective theory at high temperature is also computed to the same order. Existing calculations are reproduced and new results are obtained in the quark sector for which only partial results existed up to dimension six.

hep-ph↗
arXiv2003

The Spectral Quark Model and Light Cone Phenomenology

Chiral quark models offer a practical and simple tool to describe covariantly both low and high energy phenomenology in combination with QCD evolution. This can be done in full harmony with chiral symmetry and electromagnetic gauge invariance. We review the recently proposed spectral quark model where all these constraints are implemented.

hep-ph↗
arXiv2003

Renormalization of Singlet NN-Scattering with One Pion Exchange and Boundary Conditions

We present a simple and physically compelling boundary condition regularization scheme in the framework of effective field theory as applied to nucleon-nucleon interaction. It is free of off-shell ambiguities and ultraviolet divergences and provides finite results at any step of the calculation. Low energy constants and their non-perturbative evolution can directly be obtained from experimental threshold parameters in a completely unique and model independent way when the long range explicit pion effects are removed. This allows to compute scattering phase shifts which are, by construction consistent with effective range expansion to a given order in the CM momentum and are free from finite cut-off artifacts. We illustrate how the method works in the $^1S_0$ channel for the One Pion Exchange potential.

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arXiv2003

Chiral Symmetry and s-wave Low-Lying Meson-Baryon Resonances

The $s-$wave meson-baryon scattering is analyzed for the isospin-strangeness $I=1/2, S=0$ and $I=0,S=-1$ sectors, in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. For both sectors, four channels have been considered: $πN$, $ηN$, $K Λ$, $K Σ$ and $πΣ$, $\bar K N$, $ηΛ$, $K Ξ$, respectively. The needed two particle irreducible matrix amplitudes are taken from lowest order Chiral Perturbation Theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the available data: elastic $πN $ phase-shifts, $π^- p \to ηn$ and $π^- p \to K^0 Λ$ cross sections and to $πΣ\toπΣ$ mass-spectrum, the elastic $\bar K N \to \bar K N$ and $ \bar K N\to πΣ$ $t$--matrices and to the $ K^- p \to ηΛ$ cross section data. The position and residues of the complex poles in the second Riemann sheet of the scattering amplitude determine masses, widths and branching ratios of the $S_{11}-$ $N$(1535) and $-N$(1650) and $S_{01}-$ $Λ$(1405) and $-Λ$(1670) resonances, in reasonable agreement with experiment. A good overall description of data, from threshold up to around 2 GeV is achieved despite the fact that three-body channels have not been explicitly included.

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arXiv2003

$S=-1$ Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory and the $S_{01}-$ $Λ$(1405) and $- Λ$(1670) Resonances

The $s-$wave meson-baryon scattering is analyzed for the strangeness $S=-1$ and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four channels have been considered: $πΣ$, $\bar K N$, $ηΛ$ and $K Ξ$. The required input to solve the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the $πΣ\toπΣ$ mass-spectrum, to the elastic $\bar K N \to \bar K N$ and $ \bar K N\to πΣ$ $t$--matrices and to the $ K^- p \to ηΛ$ cross section data. The position and residues of the complex poles in the second Riemann Sheet of the scattering amplitude determine masses, widths and branching ratios of the $S_{01}-$ $Λ$(1405) and $-Λ$(1670) resonances, in reasonable agreement with experiment. A good overall description of data, from $πΣ$ threshold up to 1.75 GeV, is achieved despite the fact that three-body channels have not been explicitly included.

hep-ph↗
arXiv2002

The Polyakov loop and the heat kernel expansion at finite temperature

The lower order terms of the heat kernel expansion at coincident points are computed in the context of finite temperature quantum field theory for flat space-time and in the presence of general gauge and scalar fields which may be non Abelian and non stationary. The computation is carried out in the imaginary time formalism and the result is fully consistent with invariance under topologically large and small gauge transformations. The Polyakov loop is shown to play a fundamental role.

hep-th↗
arXiv2002

Meson-Baryon Interactions in Unitarized Chiral Perturbation Theory

Meson-Baryon Interactions can be successfully described using both Chiral Symmetry and Unitarity. The $s-$wave meson-baryon scattering amplitude is analyzed in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry in the potential. Two body coupled channel unitarity is exactly preserved. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. Off-shell behavior is parameterized in terms of low energy constants. The relation to the heavy baryon limit is discussed. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths baryonic resonances of the N(1535), N(1670), $Λ(1405)$ and $Λ(1670)$ resonances which compare well with accepted numbers.

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arXiv2002

Pion Structure at High and Low Energies in Chiral Quark Models

Low and high energy properties of the pion are reviewed in the framework of chiral quark models. Particular emphasis is put on the simplest version of the SU(2) NJL model as prototype. The role of gauge invariance in this kind of calculations is stressed. The results are used as initial conditions for perturbative QCD evolution equations. At leading order the quark model scale is $μ_0 \sim 320 {\rm MeV} $ as determined from the pion distribution functions and the pion distribution amplitudes.

hep-ph↗
arXiv2002

S=--1 Meson-Baryon Scattering in Coupled Channel Unitarized Chiral Perturbation Theory

The $s-$wave meson-baryon scattering amplitude is analyzed for the strangeness $S=-1$ and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four two-body channels have been considered: $\bar K N$, $πΣ$, $ηΛ$, $ K Ξ$. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. Off-shell behaviour is parameterized in terms of low energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths of the $Λ(1405)$ and $Λ(1670)$ resonances which compare well with accepted numbers.

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arXiv2001

Parton Distributions Functions of Pion, Kaon and Eta pseudoscalar mesons in the NJL model

Parton distributions of pseudoscalar pi,K and eta mesons obtained within the NJL model using the Pauli-Villars regularization method are analyzed in terms of LO and NLO evolution, and the valence sea quark and gluon parton distributions for the pion are obtained at Q^2 = 4 GeV^2 and compared to existing parametrizations at that scale. Surprisingly, the NLO order effects turn out to be small compared to the LO ones. The valence distributions are in good agreement with experimental analyses, but the gluon and sea distributions come out to be softer in the high-x region and harder in the low-x region than the experimental analyses suggest.

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