6,283 research outputs found
Probing the effectiveness: chiral perturbation theory calculations of low-energy electromagnetic reactions on deuterium
I summarize three recent calculations of electromagnetic reactions on
deuterium in chiral perturbation theory. All of these calculations were carried
out to O(Q^4), i.e. next-to-next-to-leading order. The reactions discussed here
are: elastic electron-deuteron scattering, Compton scattering on deuterium, and
the photoproduction of neutral pions from deuterium at threshold.Comment: 12 pages, 9 figures. Contribution to conference on "Mesons and Light
Nuclei". To appear in the proceeding
Recent results in chiral effective field theory for the NN system
I describe recent progress towards a theory of the NN force which captures
the consequences of QCD's chiral symmetry and the pattern of its breaking, and
is formulated as an expansion in a ratio of low and high mass scales,
M_{lo}/M_{hi}. This "chiral effective field theory" of the NN system is a firm
foundation for explorations of nuclear structure and reactions that are
grounded in QCD's low-energy symmetries. While calculations that use a ChiPT
expansion for the NN potential have proven very successful, they can only be
used with a narrow range of momentum-space cutoffs, which leaves the expansion
parameter for observable quantities somewhat murky. Here we seek a truly
systematic effective field theory for the NN amplitude, that is manifestly
renormalization-group invariant at each order in a demonstrably perturbative
expansion.Comment: Invited talk at the 7th International Workshop on Chiral Dynamics,
August 6-10, 2012, Jefferson Lab, Newport News, VA. To appear in the
proceedings. 12 pages, 5 figure
The nucleon-nucleon system in chiral effective theory
I discuss the conditions under which the application of chiral perturbation
theory to the NN potential gives reliable results for NN scattering phase
shifts. ChiPT also yields a convergent expansion for the deuteron charge
operator. For cutoffs < 1 GeV, this produces precise predictions for
deuterium's quadrupole and charge form factors in the range Q^2 < 0.25 GeV^2.Comment: 4 pages, 4 figures. Contribution to Proceedings of "12th
International Conference on Meson-Nucleon Physics and the Structure of the
Nucleon", Williamsburg, VA, May 31-June 4, 201
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 meson-exchange current is
included. The experimentally-measured quantities , , and 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.Comment: 17 pages, 4 figures, uses BoxedEPS.tex, lamuphys.sty, bibnorm.sty. To
appear in the proceedings of the Workshop on Electron-Nucleus Scattering held
at the Elba International Physics Center, June 199
Properties of Lithium-11 and Carbon-22 at leading order in halo effective field theory
We study the and nuclei at leading order
(LO) in halo effective field theory (Halo EFT). Using the value of the
rms matter radius deduced in Ref. [1] as an input in a LO
calculation, we simultaneously constrained the values of the two-neutron (2)
separation energy of and the virtual-state energy of the
neutron system (hereafter denoted C). The 1
uncertainty of the input rms matter radius datum, along with the theory error
estimated from the anticipated size of the higher-order terms in the Halo EFT
expansion, gave an upper bound of about 100 keV for the 2 separation energy.
We also study the electric dipole excitation of 2 halo nuclei to a continuum
state of two neutrons and the core at LO in Halo EFT. We first compare our
results with the data from a Coulomb dissociation experiment
and obtain good agreement within the theoretical uncertainty of a LO
calculation. We then obtain the low-energy spectrum of of this
transition at several different values of the 2 separation energy of
and the virtual-state energy of . Our
predictions can be compared to the outcome of an ongoing experiment on the
Coulomb dissociation of to obtain tighter constraints on the
two- and three-body energies in the system.Comment: 6 pages, 3 figures; Contribution to the 21st International Conference
on Few-Body Problems in Physic
Effects of Inhomogeneity on the Causal Entropic prediction of Lambda
The causal entropic principle aims to predict the unexpectedly small value of
the cosmological constant Lambda using a weighting by entropy increase on
causal diamonds. The original work assumed a purely isotropic and homogeneous
cosmology. But even the level of inhomogeneity observed in our universe forces
reconsideration of certain arguments about entropy production. In particular,
we must consider an ensemble of causal diamonds associated with one cosmology,
and we can no longer immediately discard entropy production in the far future
of the universe. Depending on our choices for a probability measure and our
treatment of black hole evaporation, the prediction for Lambda may be left
intact or dramatically altered.Comment: 9 pages, 5 figures. V2: appearing in Phys Rev. D, including
additional discussion of generic late-time entropy sources and a more general
calculation of their effects on the prediction for \Lambda, along with an
updated figur
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