390 research outputs found
The two-nucleon electromagnetic charge operator in chiral effective field theory (EFT) up to one loop
The electromagnetic charge operator in a two-nucleon system is derived in
chiral effective field theory (EFT) up to order (or N4LO), where
denotes the low-momentum scale and is the electric charge. The specific
form of the N3LO and N4LO corrections from, respectively, one-pion-exchange and
two-pion-exchange depends on the off-the-energy-shell prescriptions adopted for
the non-static terms in the corresponding potentials. We show that different
prescriptions lead to unitarily equivalent potentials and accompanying charge
operators. Thus, provided a consistent set is adopted, predictions for physical
observables will remain unaffected by the non-uniqueness associated with these
off-the-energy-shell effects.Comment: 16 pages, 10 figure
Electromagnetic Structure and Reactions of Few-Nucleon Systems in EFT
We summarize our recent work dealing with the construction of the
nucleon-nucleon potential and associated electromagnetic currents up to one
loop in chiral effective field theory (EFT). The magnetic dipole
operators derived from these currents are then used in hybrid calculations of
static properties and low-energy radiative capture processes in few-body
nuclei. A preliminary set of results are presented for the magnetic moments of
the deuteron and trinucleons and thermal neutron captures on , , and
He.Comment: Invited talk to the 19th International IUPAP Conference on Few-Body
Problems in Physic
Electromagnetic processes in a EFT framework
Recently, we have derived a two--nucleon potential and consistent nuclear
electromagnetic currents in chiral effective field theory with pions and
nucleons as explicit degrees of freedom. The calculation of the currents has
been carried out to include NLO corrections, consisting of two--pion
exchange and contact contributions. The latter involve unknown low-energy
constants (LECs), some of which have been fixed by fitting the S- and
P-wave phase shifts up to 100 MeV lab energies. The remaining LECs entering the
current operator are determined so as to reproduce the experimental deuteron
and trinucleon magnetic moments, as well as the cross section. This
electromagnetic current operator is utilized to study the and He
radiative captures at thermal neutron energies. Here we discuss our results
stressing on the important role played by the LECs in reproducing the
experimental data.Comment: Invited talk at the 5th International Conference on Quarks and
Nuclear Physics, to appear in Chinese Physics
Electromagnetic structure of A=2 and 3 nuclei in chiral effective field theory
The objectives of the present work are twofold. The first is to address and
resolve some of the differences present in independent,
chiral-effective-field-theory (\chiEFT) derivations up to one loop, recently
appeared in the literature, of the nuclear charge and current operators. The
second objective is to provide a complete set of \chiEFT predictions for the
structure functions and tensor polarization of the deuteron, for the charge and
magnetic form factors of 3He and 3H, and for the charge and magnetic radii of
these few-nucleon systems. The calculations use wave functions derived from
high-order chiral two- and three-nucleon potentials and Monte Carlo methods to
evaluate the relevant matrix elements. Predictions based on conventional
potentials in combination with \chiEFT charge and current operators are also
presented. There is excellent agreement between theory and experiment for all
these observables for momentum transfers up to q< 2.0-2.5 (1/fm); for a subset
of them, this agreement extends to momentum transfers as high as q~5-6 (1/fm).
A complete analysis of the results is provided.Comment: 34 pages, Revte
A chiral effective field theory study of hadronic parity violation in few-nucleon systems
We reconsider the derivation of the nucleon-nucleon parity-violating (PV)
potential within a chiral effective field theory framework. We construct the
potential up to next-to-next-to-leading order by including one-pion-exchange,
two-pion-exchange, contact, and 1/M (M being the nucleon mass) terms, and use
dimensional regularization to renormalize the pion-loop corrections. A detailed
analysis of the number of independent low-energy constants (LEC's) entering the
potential is carried out. We find that it depends on six LEC's: the
pion-nucleon PV coupling constant and five parameters multiplying
contact interactions. We investigate PV effects induced by this potential on
several few-nucleon observables, including the - longitudinal
asymmetry, the neutron spin rotation in - and -
scattering, and the longitudinal asymmetry in the HeH
charge-exchange reaction. An estimate for the range of values of the various
LEC's is provided by using available experimental data.Comment: 31 pages, 7 figures, submitted to Physical Review
Thermal neutron captures on and He
We report on a study of the and n\,^3He radiative captures at thermal
neutron energies, using wave functions obtained from either chiral or
conventional two- and three-nucleon realistic potentials with the
hyperspherical harmonics method, and electromagnetic currents derived in chiral
effective field theory up to one loop. The predicted and n\,^3He cross
sections are in good agreement with data, but exhibit a significant dependence
on the input Hamiltonian. A comparison is also made between these and new
results for the and n\,^3He cross sections obtained in the conventional
framework for both potentials and currents.Comment: 4 pages, 4 eps figures; references added; corrections to text and
abstract as suggested by referee adde
Tritium -decay in chiral effective field theory
We evaluate the Fermi and Gamow-Teller (GT) matrix elements in tritium
-decay by including in the charge-changing weak current the corrections
up to one loop recently derived in nuclear chiral effective field theory
( EFT). The trinucleon wave functions are obtained from
hyperspherical-harmonics solutions of the Schrodinger equation with two- and
three-nucleon potentials corresponding to either EFT (the N3LO/N2LO
combination) or meson-exchange phenomenology (the AV18/UIX combination). We
find that contributions due to loop corrections in the axial current are, in
relative terms, as large as (and in some cases, dominate) those from one-pion
exchange, which nominally occur at lower order in the power counting. We also
provide values for the low-energy constants multiplying the contact axial
current and three-nucleon potential, required to reproduce the experimental GT
matrix element and trinucleon binding energies in the N3LO/N2LO and AV18/UIX
calculations.Comment: 19 pages,6 figures, corrections to Text as suggested by Referee
added; Erratum: 4 pages, 3 figures, corrections to Eq.(20), Tables I, II,
III, Figures 4, 5, conclusions unchange
Minimally non-local nucleon-nucleon potentials with chiral two-pion exchange including 's
We construct a coordinate-space chiral potential, including -isobar
intermediate states in its two-pion-exchange component. The contact
interactions entering at next-to-leading and next-to-next-to-next-to-leading
orders ( and , respectively, denoting generically the low
momentum scale) are rearranged by Fierz transformations to yield terms at most
quadratic in the relative momentum operator of the two nucleons. The low-energy
constants multiplying these contact interactions are fitted to the 2013 Granada
database, consisting of 2309 and 2982 data (including, respectively,
148 and 218 normalizations) in the laboratory-energy range 0--300 MeV. For the
total 5291 and data in this range, we obtain a /datum of
roughly 1.3 for a set of three models characterized by long- and short-range
cutoffs, and respectively, ranging from fm down to fm. The long-range
(short-range) cutoff regularizes the one- and two-pion exchange (contact) part
of the potential.Comment: 32 pages, 19 figures, accepted for publication as a Regular Article
in Physical Review
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