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Daniel R. Phillips

Publications and source records attributed to Daniel R. Phillips.

84 records · Page 5Linked to original sources
arXiv2003

Higher-order calculations of electron-deuteron scattering in nuclear effective theory

Motivated by recent advances in the application of effective field theory techniques to light nuclei we revisit the problem of electron-deuteron scattering in these approaches. By sidestepping problems with the description of electron-nucleon scattering data in effective field theories, we show that the effective theory expansion for deuteron physics converges well over a wide range of momentum transfers. The resultant description of the physics of the two-nucleon system is good up to virtual photon momenta of order 700 MeV.

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arXiv2003

Effective theory of the Delta(1232) in Compton scattering off the nucleon

We formulate a new power-counting scheme for a chiral effective field theory of nucleons, pions, and Deltas. This extends chiral perturbation theory into the Delta-resonance region. We calculate nucleon Compton scattering up to next-to-leading order in this theory. The resultant description of existing $γ$p cross section data is very good for photon energies up to about 300 MeV. We also find reasonable numbers for the spin-independent polarizabilities $α_p$ and $β_p$.

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arXiv2001

The likelihood of GODs' existence: Improving the SN1987a constraint on the size of large compact dimensions

The existence of compact dimensions which are accessible only to gravity represents an intriguing possible solution to the hierarchy problem. At present the strongest constraint on the existence of such compact Gravity-Only Dimensions (GODs) comes from SN1987a. Here we report on the first self-consistent simulations of the early, neutrino-emitting phase of a proto-neutron star which include energy losses due to the coupling of the Kaluza-Klein modes of the graviton which arise in a world with GODs. We compare the neutrino signals from these simulations to that from SN1987a and use a rigorous probabilistic analysis to derive improved bounds for the radii of such GODs. We find that the possibility that there are two compact extra dimensions with radii larger than 0.66 $μ$m is excluded at the 95% confidence level---as is the possibility that there are three compact extra dimensions larger than 0.8 nm.

astro-ph↗
arXiv2000

From Hadrons to Nuclei: Crossing the Border

The study of nuclei predates by many years the theory of quantum chromodynamics. More recently, effective field theories have been used in nuclear physics to ``cross the border'' from QCD to a nuclear theory. We are now entering the second decade of efforts to develop a perturbative theory of nuclear interactions using effective field theory. This work describes the current status of these efforts.

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arXiv2000

Extra dimensions, SN1987a, and nucleon-nucleon scattering data

One of the strongest constraints on the existence of large, compact, "gravity-only" dimensions comes from SN1987a. If the rate of energy loss into these putative extra dimensions is too high, then the neutrino pulse from the supernova will differ from that actually seen. The dominant mechanism for the production of Kaluza-Klein gravitons and dilatons in the supernova is via gravistrahlung and dilastrahlung from the nucleon-nucleon system. In this paper we compute the rates for these processes in a model-independent way using low-energy theorems which relate the emissivities to the measured nucleon-nucleon cross section. This is possible because for soft gravitons and dilatons the leading contribution to the energy-loss rate is from graphs in which the gravitational radiation is produced from external nucleon legs. Previous calculations neglected these mechanisms. We re-evaluate the bounds on toroidally-compactified "gravity-only" dimensions (GODs), and find that consistency with the observed SN1987a neutrino signal requires that if there are two such dimensions then their radius must be less than 1 micron.

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arXiv2000

Neutrino and axion emissivities of neutron stars from nucleon-nucleon scattering data

Neutrino and axion production in neutron stars occurs mainly as bremsstrahlung from nucleon-nucleon (NN) scattering. The energy radiated via neutrinos or axions is typically very small compared to other scales in the two-nucleon system. The rate of emission of such "soft" radiation is directly related to the on-shell NN amplitude, and thereby to the NN experimental data. This facilitates the model-independent calculation of the neutrino and axion radiation rates which is presented here. We find that the resultant rates are a factor of four below earlier estimates based on a one-pion-exchange NN amplitude.

astro-ph↗
arXiv2000

Restoration of rotational invariance of bound states on the light front

We study bound states in a model with scalar nucleons interacting via an exchanged scalar meson using the Hamiltonian formalism on the light front. In this approach manifest rotational invariance is broken when the Fock space is truncated. By considering an effective Hamiltonian that takes into account two meson exchanges, we find that this breaking of rotational invariance is decreased from that which occurs when only one meson exchange is included. The best improvement occurs when the states are weakly bound.

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arXiv1999

Improving the Convergence of NN Effective Field Theory

We study a low-energy effective field theory (EFT) describing the NN system in which all exchanged particles are integrated out. We show that fitting the residue of the 3S1 amplitude at the deuteron pole, rather than the 3S1 effective range, dramatically improves the convergence of deuteron observables in this theory. Reproducing the residue ensures that the tail of the deuteron wave function, which is directly related to NN scattering data via analytic continuation, is correctly reproduced in the EFT at next-to-leading order. The role of multi-nucleon-electroweak operators which produce deviations from effective-range theory can then be explicitly separated from the physics of the wave function tail. Such an operator contributes to the deuteron quadrupole moment, mu_Q, at low order, indicating a sensitivity to short-distance physics. This is consistent with the failure of impulse approximation calculations in NN potential models to reproduce mu_Q. The convergence of NN phase shifts in the EFT is unimpaired by the use of this new expansion.

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arXiv1998

Electron-deuteron scattering in a relativistic theory of hadrons

We review a three-dimensional formalism that provides a systematic way to include relativistic effects including relativistic kinematics, the effects of negative-energy states, and the boosts of the two-body system in calculations of two-body bound-states. We then explain how to construct a conserved current within this relativistic three-dimensional approach. This general theoretical framework is specifically applied to electron-deuteron scattering both in impulse approximation and when the $ρπγ$ meson-exchange current is included. The experimentally-measured quantities $A$, $B$, and $T_{20}$ are calculated over the kinematic range that is probed in Jefferson Lab experiments. The role of both negative-energy states and meson retardation appears to be small in the region of interest.

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arXiv1997

Non-perturbative regularization and renormalization: simple examples from non-relativistic quantum mechanics

We examine several zero-range potentials in non-relativistic quantum mechanics. The study of such potentials requires regularization and renormalization. We contrast physical results obtained using dimensional regularization and cutoff schemes and show explicitly that in certain cases dimensional regularization fails to reproduce the results obtained using cutoff regularization. First we consider a delta-function potential in arbitrary space dimensions. Using cutoff regularization we show that for $d \ge 4$ the renormalized scattering amplitude is trivial. In contrast, dimensional regularization can yield a nontrivial scattering amplitude for odd dimensions greater than or equal to five. We also consider a potential consisting of a delta function plus the derivative-squared of a delta function in three dimensions. We show that the renormalized scattering amplitudes obtained using the two regularization schemes are different. Moreover we find that in the cutoff-regulated calculation the effective range is necessarily negative in the limit that the cutoff is taken to infinity. In contrast, in dimensional regularization the effective range is unconstrained. We discuss how these discrepancies arise from the dimensional regularization prescription that all power-law divergences vanish. We argue that these results demonstrate that dimensional regularization can fail in a non-perturbative setting.

hep-th↗
arXiv1996

How short is too short? Constraining zero-range interactions in nucleon-nucleon scattering

We discuss a number of constraints on the effects of zero-range potentials in quantum mechanics. We show that for such a potential $p \cot(δ)$, where $p$ is the momentum of the nucleon in the center of mass frame and $δ$ is the S-wave phase shift, must be a monotonically decreasing function of energy. This implies that the effective range of the potential is non-positive. We also examine scattering from the sum of two potentials, one of which is a short-range interaction. We find that if the short-range interaction is of zero-range then it must be attractive, and the logarithmic derivative of the radial wave function at the origin must be a monotonically decreasing function of energy. If the short-range interaction is not of zero range then a constraint which gives the minimum possible range for it to fit the phase shifts exists. The implications of these results for effective field theory treatments of nucleon-nucleon interactions are discussed.

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