13,486 research outputs found
Dominant -exchange nucleon-nucleon interaction: Spin-spin and tensor potentials
We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the two-pion exchange nucleon-nucleon
interaction that is generated by the isovector spin-flip
contact-vertex proportional to the large low-energy constant GeV. We find that the respective -exchange potentials
contain sizeable isospin-breaking components which reach up to -4% of
corresponding isovector -exchange potentials. The typical values of these
novel charge-independence breaking spin-spin and tensor potentials are MeV and MeV, at a nucleon distance of fm. The
charge-symmetry breaking spin-spin and tensor potentials come out a factor of
2.4 smaller. Our analytical results for these presumably dominant
isospin-violating spin-spin and tensor NN-forces are in a form such that they
can be easily implemented into phase-shift analyses and few-body calculations.Comment: 7 pages, 1 figure, 2 tables, to be published in Physical Review C:
Brief report
Electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon potential
We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon
interaction that is generated by the isoscalar contact-vertex
proportional to the large low-energy constant . We find that the
respective -exchange potential contains sizeable isospin-breaking
components which amount to about -1% of the strongly attractive isoscalar
central -exchange potential. The typical value of these novel
charge-independence and charge-symmetry breaking central potentials is MeV at a nucleon distance of fm. Our analytical result
for this presumably dominant -exchange interaction is in a form
such that it can be easily implemented into phase-shift analyses and few-body
calculations.Comment: 7 pages, 1 figure, to be published in Physical Review C (2006): Brief
Report
Nuclear energy density functional from chiral pion-nucleon dynamics: Isovector terms
We extend a recent calculation of the nuclear energy density functional in
the framework of chiral perturbation theory by computing the isovector surface
and spin-orbit terms: (\vec \nabla \rho_p- \vec \nabla \rho_n)^2 G_d(\rho)+
(\vec \nabla \rho_p- \vec \nabla \rho_n)\cdot(\vec J_p-\vec J_n)
G_{so(\rho)+(\vec J_p-\vec J_n)^2 G_J(\rho) pertaining to different proton and
neutron densities. Our calculation treats systematically the effects from
-exchange, iterated -exchange, and irreducible -exchange with
intermediate -isobar excitations, including Pauli-blocking corrections
up to three-loop order. Using an improved density-matrix expansion, we obtain
results for the strength functions , and
which are considerably larger than those of phenomenological Skyrme forces.
These (parameter-free) predictions for the strength of the isovector surface
and spin-orbit terms as provided by the long-range pion-exchange dynamics in
the nuclear medium should be examined in nuclear structure calculations at
large neutron excess.Comment: 12 pages, 5 figure
Chiral 3-exchange NN-potentials: Results for dominant next-to-leading order contributions
We calculate in (two-loop) chiral perturbation theory the local NN-potentials
generated by the three-pion exchange diagrams with one insertion from the
second order chiral effective pion-nucleon Lagrangian proportional to the
low-energy constants . The resulting isoscalar central potential
vanishes identically. In most cases these -exchange potentials are larger
than the ones generated by the diagrams involving only leading order vertices
due to the large values of (which mainly represent virtual
-excitation). A similar feature has been observed for the chiral
-exchange. We also give suitable (double-integral) representations for
the spin-spin and tensor potentials generated by the leading-order diagrams
proportional to involving four nucleon propagators. In these cases the
Cutkosky rule cannot be used to calculate the spectral-functions in the
infinite nucleon mass limit since the corresponding mass-spectra start with a
non-vanishing value at the -threshold. Altogether, one finds that chiral
-exchange leads to small corrections in the region fm where
- and chiral -exchange alone provide a very good strong NN-force as
shown in a recent analysis of the low-energy pp-scattering data-base.Comment: 11 pages, 7 figures, to be published in The Physical Review
Nuclear energy density functional from chiral pion-nucleon dynamics: Isovector spin-orbit terms
We extend a recent calculation of the nuclear energy density functional in
the systematic framework of chiral perturbation theory by computing the
isovector spin-orbit terms: . The calculation
includes the one-pion exchange Fock diagram and the iterated one-pion exchange
Hartree and Fock diagrams. From these few leading order contributions in the
small momentum expansion one obtains already a good equation of state of
isospin-symmetric nuclear matter. We find that the parameterfree results for
the (density-dependent) strength functions and agree
fairly well with that of phenomenological Skyrme forces for densities . At very low densities a strong variation of the strength functions
and with density sets in. This has to do with chiral
singularities and the presence of two competing small mass scales
and . The novel density dependencies of and
as predicted by our parameterfree (leading order) calculation should
be examined in nuclear structure calculations.Comment: 9 pages, 3 figure, published in: Physical Review C68, 014323 (2003
Radiative corrections to neutral pion-pair production
We calculate the one-photon loop radiative corrections to the neutral
pion-pair photoproduction process . At leading
order this reaction is governed by the chiral pion-pion interaction. Since the
chiral contact-vertex depends only on the final-state
invariant-mass it factors out of all photon-loop diagrams. We give analytical
expressions for the multiplicative correction factor
arising from eight classes of contributing one-photon loop diagrams. An
electromagnetic counterterm has to be included in order to cancel the
ultraviolet divergences generated by the photon-loops. Infrared finiteness of
the virtual radiative corrections is achieved (in the standard way) by
including soft photon radiation below an energy cut-off . The
radiative corrections to the total cross section vary between and
for center-of-mass energies from threshold up to . The finite part of
the electromagnetic counterterm gives an additional constant contribution of
about , however with a large uncertainty.Comment: 10 pages, 6 figures, submitted to Eur. Phys. J.
Scales in nuclear matter: Chiral dynamics with pion nucleon form factors
A systematic calculation of nuclear matter is performed which includes the
long-range correlations between nucleons arising from one- and two-pion
exchange. Three-body effects from -exchange with excitations of virtual
-isobars are also taken into account in our diagrammatic
calculation of the energy per particle . In order to eliminate
possible high-momentum components from the interactions we introduce at each
pion-baryon vertex a form factor of monopole type. The empirical nuclear matter
saturation point, fm, MeV, is
well reproduced with a monopole mass of GeV. As in the recent approach based on the universal low-momentum
-potential , the inclusion of three-body effects is crucial
in order to achieve saturation of nuclear matter. We demonstrate that the
dependence of the pion-exchange contributions to on the
''resolution'' scale can be compensated over a wide range of
by counterterms with two ''running'' contact-couplings. As a further
application we study the in-medium chiral condensate beyond
the linear density approximation. For we find small
corrections from the derivative , which are stable
against variations of the monopole regulator mass .Comment: 13 pages, 6 figure
General Relativistic Description of the Observed Galaxy Power Spectrum: Do We Understand What We Measure?
We extend the general relativistic description of galaxy clustering developed
in Yoo, Fitzpatrick, and Zaldarriaga (2009). For the first time we provide a
fully general relativistic description of the observed matter power spectrum
and the observed galaxy power spectrum with the linear bias ansatz. It is
significantly different from the standard Newtonian description on large scales
and especially its measurements on large scales can be misinterpreted as the
detection of the primordial non-Gaussianity even in the absence thereof. The
key difference in the observed galaxy power spectrum arises from the real-space
matter fluctuation defined as the matter fluctuation at the hypersurface of the
observed redshift. As opposed to the standard description, the shape of the
observed galaxy power spectrum evolves in redshift, providing additional
cosmological information. While the systematic errors in the standard Newtonian
description are negligible in the current galaxy surveys at low redshift,
correct general relativistic description is essential for understanding the
galaxy power spectrum measurements on large scales in future surveys with
redshift depth z>3. We discuss ways to improve the detection significance in
the current galaxy surveys and comment on applications of our general
relativistic formalism in future surveys.Comment: accepted for publication in Physical Review
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