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Martin J. Savage

Publications and source records attributed to Martin J. Savage.

At least 163 records · Page 9Linked to original sources
arXiv1999

Isoscalar M1 and E2 Amplitudes in n+p -> d+gamma

The low energy radiative capture process n+p -> d+gamma provides a sensitive probe of the two-nucleon system. The cross section for this process is dominated by the isovector M1 amplitude for capture from the 1S0 channel via the isovector magnetic moment of the nucleon. In this work we use effective field theory to compute the isoscalar M1 and isoscalar E2 amplitudes that are strongly suppressed for cold neutron capture. The actual value of the isoscalar E2 amplitude is expected to be within 15% of the value computed in this work. In contrast, due to the vanishing contribution of the one-body operator at leading order and next-to-leading order, the isoscalar M1 amplitude is estimated to have a large uncertainty. We discuss in detail the deuteron quadrupole form factor and SD mixing.

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arXiv1999

The Anapole Form Factor of the Deuteron

We find the leading order result for the anapole form factor of the deuteron using effective field theory. The momentum dependence of the anapole form factor is different from that of the matrix element of the strange currents in the deuteron, which may provide a way for disentangling these two competing effects when analyzing parity violating electron-deuteron scattering experiments. We give closed form expressions for both the form factor and integrals often encountered in the NN effective field theory.

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arXiv1999

n+p -> d+gamma for Big-Bang Nucleosynthesis

The cross section for n+p -> d+gamma is calculated at energies relevant to big bang nucleosynthesis using the recently developed effective field theory that describes the two-nucleon sector. The E1 amplitude is computed up to NNNLO and depends only upon nucleon-nucleon phase shift data. In contrast, the M1 contribution is computed up to NLO, and the four-nucleon-one-magnetic-photon counterterm that enters is determined by the cross section for cold neutron capture. The uncertainty in the calculation for nucleon energies up to E ~ 1 MeV is estimated to be < 4%.

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arXiv1999

Nucleon-Nucleon Effective Field Theory Without Pions

Nuclear processes involving momenta much below the mass of the pion may be described by an effective field theory in which the pions do not appear as explicit degrees of freedom. The effects of the pion and all other virtual hadrons are reproduced by the coefficients of gauge-invariant local operators involving the nucleon field. Nucleon-nucleon scattering phase shift data constrains many of the coefficients that appear in the effective Lagrangean but at some order in the expansion coefficients enter that must be constrained by other observables. We compute several observables in the two-nucleon sector up to next-to-next-to leading order in the effective field theory without pions, or to the order at which a counterterm involving four-nucleon field operators is encountered. Effective range theory is recovered from the effective field theory up to the order where relativistic corrections enter or where four-nucleon-external current local operators arise. For the deuteron magnetic moment, quadrupole moment and the $np\to dγ$ radiative capture cross section a four-nucleon-one-photon counterterm exists at next-to-leading order. The electric polarizability and electric charge form factor of the deuteron are determined up to next-to-next-to-leading order, which includes the first appearance of relativistic corrections.

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arXiv1999

Parity Violation in Effective Field Theory and the Deuteron Anapole Moment

Effective field theory, including pions, provides a consistent and systematic description of nucleon-nucleon strong interactions up to center-of-mass momentum of order 300 MeV per nucleon. We describe the inclusion of hadronic parity violation into this effective field theory and find an analytic form for the deuteron anapole moment at leading order in the expansion.

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arXiv1999

The Two-Nucleon Sector with Effective Field Theory

I present the results obtained for several observables in the two-nucleon sector using effective field theory with KSW power-counting and dimensional regularization. In addition to the phase shifts for nucleon-nucleon scattering, several deuteron observables are discussed, including electromagnetic form factors, polarizabilities, gamma+d -> gamma+d Compton scattering, and n+p -> d+gamma. A detailed comparison between the effective field theory with pions, the theory without pions, and effective range theory is made.

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arXiv1998

Pionic Matrix Elements in Neutrinoless Double-Beta Decay

Physics beyond the standard model of electroweak interactions that violates lepton number will, in general, induce operators involving the quark and lepton fields that violate lepton number. I point out that some matrix elements of particular operators are known. In the limit of exact SU(3) flavor symmetry the operator overline{u} gamma_mu (1-gamma_5)d overline{u} gamma_mu (1-gamma_5)d is part of the ${\bf 27}$ representation responsible for Delta I=3/2 strangeness changing decays in the standard model. At leading order in the chiral expansion there is only one coupling constant that describes the weak interactions of the pseudo-Goldstone bosons induced by the 27 representation. The observed branching fraction for K+ to pi+ pi0 determines this coupling constant. Contributions of the form m_s log m_s are used to estimate SU(3) breaking corrections to the relation between K+ to pi+ pi0 and the pi- to pi+ e- e- interaction.

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arXiv1998

A Perturbative Calculation of the Electromagnetic Form Factors of the Deuteron

Making use of the effective field theory expansion recently developed by the authors, we compute the electromagnetic form factors of the deuteron analytically to next-to-leading order (NLO). The computation is rather simple, and involves calculating several Feynman diagrams, using dimensional regularization. The results agree well with data and indicate that the expansion is converging. They do not suffer from any ambiguities arising from off-shell versus on-shell amplitudes.

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arXiv1998

n + p -> d + gamma in Effective Field Theory

The radiative capture process n+p-> d+gamma provides clear evidence for meson exchange currents in nuclear physics. We compute this process at low energies using a recently developed power counting for the effective field theory that describes nucleon-nucleon interactions. The leading order contribution to this process comes from the photon coupling to the nucleon magnetic moments. At subleading order there are other contributions. Among these are graphs where the photon couples directly to pions, i.e. meson exchange currents. These diagrams are divergent and require the presence of a local four-nucleon-one photon counterterm. The coefficient of this operator is determined by the measured cross section, 334.2 +- 0.5 mb, for incident neutrons with speed |v|=2200 m/s.

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arXiv1998

Gamma-Deuteron Compton Scattering in Effective Field Theory

The differential cross section for gamma-deuteron Compton scattering is computed to next-to-leading order (NLO) in an effective field theory that describes nucleon-nucleon interactions below the pion production threshold. Contributions at NLO include the nucleon isoscalar electric polarizability from its 1/m_pi behavior in the chiral limit. The parameter free prediction of the gamma-deuteron differential cross section at NLO is in good agreement with data.

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arXiv1998

An Effective Field Theory Calculation of the Parity Violating Asymmetry in n+p -> d+gamma

Weak interactions are expected to induce a parity violating pion-nucleon coupling, h_{πNN}^{(1)}. This coupling should be measurable in a proposed experiment to study the parity violating asymmetry A_γin the process \vec n + p \to d+γ. We compute the leading dependence of A_γon the coupling h_{πNN}^{(1)} using recently developed effective field theory techniques and find an asymmetry of A_γ= +0.17 h_{πNN}^{(1)} at leading order. This asymmetry has the opposite sign to that given by Desplanques, Donoghue and Holstein.

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arXiv1998

The Polarizability of the Deuteron

The scalar and tensor polarizabilities of the deuteron are calculated using the recently developed effective field theory that describes nucleon-nucleon interactions. Leading and next-to-leading order contributions in the perturbative expansion predict a scalar electric polarizability of 0.595 fm^3. The tensor electric polarizability receives contributions starting at next-to-leading order from the exchange of a single potential pion and is found to be -0.062 fm^3. We compute the leading contributions to the scalar and tensor magnetic polarizabilities, finding 0.067 fm^3 and 0.195 fm^3, respectively.

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arXiv1998

Including Pions

Recent progress in using effective field theory to describe systems with two nucleons is discussed with particular emphasis placed on the inclusion of pions. Inconsistencies arising in Weinberg's power counting are demonstrated with two concrete examples. A consistent power-counting scheme is discussed in which pion exchange is sub-leading to local four-nucleon operators. NN scattering in the 1S0 and 3S1-3D1 channels is calculated at sub-leading order and compared with data.

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arXiv1998

Two-Nucleon Systems from Effective Field Theory

We elaborate on a new technique for computing properties of nucleon-nucleon interactions in terms of an effective field theory derived from low energy NN scattering data. Details of how the expansion is carried out to higher orders are presented. Analytic formulae are given for the amplitude to subleading order in both the 1S0 and 3S1-3D1 channels.

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arXiv1998

A New Expansion for Nucleon-Nucleon Interactions

We introduce a new and well defined power counting for the effective field theory describing nucleon-nucleon interactions. Because of the large NN scattering lengths it differs from other applications of chiral perturbation theory and is facilitated by introducing an unusual subtraction scheme and renormalization group analysis. Calculation to subleading order in the expansion can be done analytically, and we present the results for both the 1S0 and 3S1-3D1 channels.

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arXiv1997

$NNK$ and $ΛΛK$ Amplitudes in Chiral Perturbation Theory

We explore the S-wave and P-wave amplitudes for $NNK$ and $ΛΛK$ interactions using chiral perturbation theory to ${\cal O}(m_s\log m_s)$. In contrast to the large corrections found in P-wave amplitudes in the nonleptonic decay of octet baryons, the $NNK$ amplitudes receive only small corrections to their tree-level values. The uncertainty in the $ΛΛK$ amplitudes is found to be large.

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arXiv1997

Hadronic and Electromagnetic Interactions of Quarkonia

We examine the hadronic interactions of quarkonia, focusing on the decays psi(2s)->psi pi pi and upsilon(2s)-> upsilon pi pi. The leading gluonic operators in the multipole expansion are matched onto the chiral lagrangian with the coefficients fit to available data, both at tree-level and loop-level in the chiral expansion. A comparison is made with naive expectations loosely based on the large-$N_c$ limit of QCD in an effort to determine the reliability of this limit for other observables, such as the binding of $\ps$ to nuclei. Crossing symmetry is used to estimate the cross-section for inelastic $π\ps\toπ\pss$ scattering, potentially relevant for heavy ion collisions. The radiative decays psi(2s)->psi pi pi gamma and upsilon(2s)-> upsilon pi pi gamma are determined at tree-level in the chiral lagrangian. Measurement of such decays will provide a test of the multipole and chiral expansions. We briefly discuss decays from the upsilon(3s) and also the contribution from pions to the electromagnetic polarizability of quarkonia.

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