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M. J. Savage

Publications and source records attributed to M. J. Savage.

28 records · Page 2Linked to original sources
arXiv2003

Two Nucleons on a Lattice

The two-nucleon sector is near an infrared fixed point of QCD and as a result the S-wave scattering lengths are unnaturally large compared to the effective ranges and shape parameters. It is usually assumed that a lattice QCD simulation of the two-nucleon sector will require a lattice that is much larger than the scattering lengths in order to extract quantitative information. In this paper we point out that this does not have to be the case: lattice QCD simulations on much smaller lattices will produce rigorous results for nuclear physics.

hep-lat↗
arXiv2003

Exploring Hyperons and Hypernuclei with Lattice QCD

In this work we outline a program for lattice QCD that would provide a first step toward understanding the strong and weak interactions of strange baryons. The study of hypernuclear physics has provided a significant amount of information regarding the structure and weak decays of light nuclei containing one or two Lambda's, and Sigma's. From a theoretical standpoint, little is known about the hyperon-nucleon interaction, which is required input for systematic calculations of hypernuclear structure. Furthermore, the long-standing discrepancies in the P-wave amplitudes for nonleptonic hyperon decays remain to be understood, and their resolution is central to a better understanding of the weak decays of hypernuclei. We present a framework that utilizes Luscher's finite-volume techniques in lattice QCD to extract the scattering length and effective range for Lambda-N scattering in both QCD and partially-quenched QCD. The effective theory describing the nonleptonic decays of hyperons using isospin symmetry alone, appropriate for lattice calculations, is constructed.

nucl-th↗
arXiv2001

Towards a Perturbative Theory of Nuclear Forces

We show that an expansion of nuclear forces about the chiral limit is formally consistent and is equivalent to KSW power counting in the 1S0 channel and Weinberg power counting in the 3S1-3D1 coupled channels. Numerical evidence suggests that this expansion converges. The feasibility of making contact between nuclear physics and lattice-QCD simulations is discussed.

nucl-th↗
arXiv1996

Kaon-Nucleon Couplings for Weak Decays of Hypernuclei

We investigate the weak kaon-nucleon (NNK) S-wave and P-wave interactions using heavy baryon chiral perturbation theory. The leading 1-loop SU(3) breaking contributions to the $ppK$, $pnK$, and $nnK$ couplings are computed. We find that they suppress all NNK amplitudes by $30\%$ to $50\%$. The ratio of neutron-induced to proton-induced hypernuclear decay widths is sensitive to such reductions. It has been argued that the discrepancy between the predicted and observed P-wave amplitudes in $Δs=1$ hyperon decay results from an accidental cancellation between tree-level amplitudes, and is not a fundamental problem for chiral perturbation theory. Agreement between experimentally determined NNK P-wave amplitudes and our estimates would support this explanation.

hep-ph↗
arXiv1993

Electromagnetic Moments of the Baryon Decuplet

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the $Ω^-$ is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large--$N_c$ limit of QCD. The leading contribution to the quadrupole moment of the $Δ$ and other members of the decuplet comes from one--loop graphs. The pionic contribution is shown to be proportional to $I_z$ (and so will not contribute to the quadrupole moment of $I=0$ nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the $SU(6)$ limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.

hep-ph↗
arXiv1993

E2/M1 Mixing Ratio of $Δ\to Nγ$ and Hyperon Resonance Radiative Decay

We compute the leading contribution to the E2/M1 mixing ratio of the decay $Δ\rightarrow Nγ$ in heavy baryon chiral perturbation theory. We find the mixing ratio to be $4\% \ltap |δ_{\rm E2/M1}| \ltap 11\%$, much larger than estimates based on the quark model and other hadronic models. We also compute the mixing ratio for the radiative decay of the hyperon resonances. The decays $Σ^{*+}\rightarrowΣ^+γ$ and $Ξ^{*-}\rightarrowΞ^-γ$ provide a particularly sensitive probe of deviations from heavy baryon spin-flavour SU(6).

hep-ph↗
arXiv1992

Chiral Perturbation Theory Analysis of the Baryon Magnetic Moments

Nonanalytic $m_q^{1/2}$ and $m_q\ln m_q$ chiral corrections to the baryon magnetic moments are computed. The calculation includes contributions from both intermediate octet and decuplet baryon states. Unlike the one-loop contributions to the baryon axial currents and masses, the contribution from decuplet intermediate states does not partially cancel that from octet intermediate states. The fit to the observed magnetic moments including $m_q^{1/2}$ corrections is found to be much worse than the tree level SU(3) fit if values for the baryon-pion axial coupling constants obtained from a tree level extraction are used. Using the axial coupling constant values extracted at one loop results in a better fit to the magnetic moments than the tree level SU(3) fit. There are three linear relations amongst the magnetic moments when $m_q^{1/2}$ corrections are included, and one relation including $m_q^{1/2}$, $m_q\ln m_q$ and $m_q$ corrections. These relations are independent of the axial coupling constants of the baryons and agree well with experiment.

hep-ph↗
arXiv1992

Radiative $D^*$ Decay Using Heavy Quark and Chiral Symmetry

The implications of chiral $SU(3)_L \times SU(3)_R$ symmetry and heavy quark symmetry for the radiative decays $D^{*0}\to D^0γ$, $D^{*+}\to D^+γ$, and $D_s^*\to D_sγ$ are discussed. Particular attention is paid to $SU(3)$ violating contributions of order $m_q^{1/2}$. Experimental data on these radiative decays provide constraints on the $D^* Dπ$ coupling.

hep-ph↗
arXiv1992

Chiral Perturbation Theory for $f_{D_S}/f_D$ and $B_{B_S}/B_{B}$

The decay constants for the $D$ and $D_S$ mesons, denoted $f_D$ and $f_{D_S}$ respectively, are equal in the $SU(3)_V$ limit, as are the hadronic amplitudes for $B_S-\bar B_S$ and $B^0-\bar B^0$ mixing. The leading $SU(3)_V$ violating contribution to $\left( f_{D_S} / f_D \right)$ and to the ratio of hadronic matrix elements relevant for $B_S-\bar B_S$ and $B^0-\bar B^0$ mixing amplitudes are calculated in chiral perturbation theory. We discuss the formalism needed to include both meson and anti-meson fields in the heavy quark effective theory.

hep-ph↗