1,513 research outputs found
Power Counting of Contact-Range Currents in Effective Field Theory
We analyze the power counting of two-body currents in nuclear effective field
theories (EFTs). We find that the existence of non-perturbative physics at low
energies, which is manifest in the existence of the deuteron and the 1S0 NN
virtual bound state, combined with the appearance of singular potentials in
versions of nuclear EFT that incorporate chiral symmetry, modifies the
renormalization-group flow of the couplings associated with contact operators
that involve nucleon-nucleon pairs and external fields. The order of these
couplings is thereby enhanced with respect to the naive-dimensional-analysis
estimate. Consequently, short-range currents enter at a lower order in the
chiral EFT than has been appreciated up until now, and their impact on
low-energy observables is concomitantly larger. We illustrate the changes in
the power counting with a few low-energy processes involving external probes
and the few-nucleon systems, including electron-deuteron elastic scattering and
radiative neutron capture by protons.Comment: 5 pages. Minor revisions. Conclusions unchanged. Version to appear in
Physical Review Letter
Power Counting and Perturbative One Pion Exchange in Heavy Meson Molecules
We discuss the possible power counting schemes that can be applied in the
effective field theory description of heavy meson molecules, such as the
X(3872) or the recently discovered Zb(10610) and Zb(10650) states. We argue
that the effect of coupled channels is suppressed by at least two orders in the
effective field theory expansion, meaning that they can be safely ignored at
lowest order. The role of the one pion exchange potential between the heavy
mesons, and in particular the tensor force, is also analyzed. By using
techniques developed in atomic physics for handling power-law singular
potentials, which have been also successfully employed in nuclear physics, we
determine the range of center-of-mass momenta for which the tensor piece of the
one pion exchange potential is perturbative. In this momentum range, the one
pion exchange potential can be considered a subleading order correction,
leaving at lowest order a very simple effective field theory consisting only on
contact-range interactions.Comment: 21 pages, 1 figur
The Heavy Quark Spin Symmetry Partners of the X(3872)
We explore the consequences of heavy quark spin symmetry for the charmed
meson-antimeson system in a contact-range (or pionless) effective field theory.
As a trivial consequence, we theorize the existence of a heavy quark spin
symmetry partner of the X(3872), with , which we call X(4012) in
reference to its predicted mass. If we additionally assume that the X(3915) is
a heavy spin symmetry partner of the X(3872), we end up predicting a
total of six molecular states. We also discuss the error
induced by higher order effects such as finite heavy quark mass corrections,
pion exchanges and coupled channels, allowing us to estimate the expected
theoretical uncertainties in the position of these new states.Comment: 18 pages; final version accepted for publicatio
Kohn-Sham calculations combined with an average pair-density functional theory
A recently developed formalism in which Kohn-Sham calculations are combined
with an ``average pair density functional theory'' is reviewed, and some new
properties of the effective electron-electron interaction entering in this
formalism are derived. A preliminary construction of a fully self-consitent
scheme is also presented in this framework.Comment: submitted to Int. J. Mod. Phys. B (proceedings of the 30th
International Workshop on Condensed Matter Theories
Renormalization of chiral two pion exchange NN interactions with delta excitations: correlations in the partial wave expansion
In this work we consider the renormalization of the chiral two-pion exchange
potential with explicit delta-excitations for nucleon-nucleon scattering at
next-to-leading (NLO) and next-to-next-to-leading order (N2LO). Due to the
singular nature of the chiral potentials, correlations between different
partial waves are generated. In particular we show that two-body scattering by
a short distance power like singular attractive interaction can be renormalized
in all partial waves with a single counterterm, provided the singularities are
identical. A parallel statement holds in the presence of tensor interactions
when the eigenpotentials in the coupled channel problem also coincide. While
this construction reduces the total number of counterterms to eleven in the
case of nucleon-nucleon scattering with chiral two-pion exchange interactions
with delta degrees of freedom, the differences in the scattering phases as
compared to the case with the uncorrelated partial wave renormalization become
smaller as the angular momentum is increased in the elastic scattering region.Comment: 20 pages, 8 figures, a section has been added discussing cut-off
dependence. Accepted for publication in PR
Deriving the existence of bound states from the X(3872) and Heavy Quark Symmetry
We discuss the possibility and the description of bound states between
and mesons. We argue that the existence of such a bound state can
be deduced from (i) the weakly bound X(3872) state, (ii) certain assumptions
about the short range dynamics of the system and (iii) heavy quark
symmetry. From these assumptions the binding energy of the possible
bound states is determined, first in a theory containing only
contact interactions which serves as a straightforward illustration of the
method, and then the effects of including the one pion exchange potential are
discussed. In this latter case three isoscalar states are predicted: a positive
and negative C-parity state with a binding energy of and below threshold respectively, and a positive C-parity
shallow state located almost at the threshold. However,
large uncertainties are generated as a consequence of the corrections
from heavy quark symmetry. Finally, the newly discovered isovector
state can be easily accommodated within the present framework by a minor
modification of the short range dynamics.Comment: 21 pages, 3 figures; a sign error in the potential has been corrected
and new predictions have been compute
Deuteron form factors in chiral effective theory: regulator-independent results and the role of two-pion exchange
We evaluate the deuteron charge, quadrupole, and magnetic form factors using
wave functions obtained from chiral effective theory (ET) when the
potential includes one-pion exchange, chiral two-pion exchange, and genuine
contact interactions. We study the manner in which the results for form factors
behave as the regulator is removed from the ET calculation, and compare
co-ordinate- and momentum-space approaches. We show that, for both the LO and
NNLO chiral potential, results obtained by imposing boundary conditions in
co-ordinate space at are equivalent to the limit of
momentum-space calculations. The regulator-independent predictions for deuteron
form factors that result from taking the limit using the
LO ET potential are in reasonable agreement with data up to momentum
transfers of order 600 MeV, provided that phenomenological information for
nucleon structure is employed. In this range the use of the NNLO ET
potential results in only small changes to the LO predictions, and it improves
the description of the zero of the charge form factor
Renormalization of NN Interaction with Relativistic Chiral Two Pion Exchange
The renormalization of the NN interaction with the Chiral Two Pion Exchange
Potential computed using relativistic baryon chiral perturbation theory is
considered. The short distance singularity reduces the number of counter-terms
to about a half as those in the heavy-baryon expansion. Phase shifts and
deuteron properties are evaluated and a general overall agreement is observed.Comment: 13 pages, 4 figures. Reference included. Typos corrected. Appendix
and discussion adde
Nucleon-Nucleon interaction, charge symmetry breaking and renormalization
We study the interplay between charge symmetry breaking and renormalization
in the NN system for s-waves. We find a set of universality relations which
disentangle explicitly the known long distance dynamics from low energy
parameters and extend them to the Coulomb case. We analyze within such an
approach the One-Boson-Exchange potential and the theoretical conditions which
allow to relate the proton-neutron, proton-proton and neutron-neutron
scattering observables without the introduction of extra new parameters and
providing good phenomenological success.Comment: 15 pages, 6 figure
- …