2,090 research outputs found
The one-pion-exchange three-nucleon force and the puzzle
We consider a new three-nucleon force generated by the exchange of one pion
in the presence of a 2N correlation. The underlying irreducible diagram has
been recently suggested by the authors as a possible candidate to explain the
puzzle of the vector analyzing powers and for nucleon-deuteron
scattering. Herein, we have calculated the elastic neutron-deuteron
differential cross section, , , , , and
below break-up threshold by accurately solving the Alt-Grassberger-Sandhas
equations with realistic interactions. We have also studied how evolves
below 30 MeV. The results indicate that this new 3NF diagram provides one
possible additional contribution, with the correct spin-isospin structure, for
the explanation of the origin of this puzzle.Comment: revised version: We have also studied how Ay evolves below 30 MeV, 4
Pages (twocolumn), 2 figures, uses psfig, RevTe
Effect of sine-Gaussian glitches on searches for binary coalescence
We investigate the effect of an important class of glitches occurring in the detector data on matched filter searches of gravitational waves from coalescing compact binaries in the advanced detector era. The glitches, which can be modeled as sine-Gaussians, can produce triggers with significant time delays and thus have important bearing on veto procedures as will be described in the paper. We provide approximated analytical estimates of the trigger SNR and time as a function of the parameters describing the sine-Gaussian (center time, center frequency and Q-factor) and the inspiral waveform (chirp mass). We validate our analytical predictions through simple numerical simulations, performed by filtering noiseless sine-Gaussians with the inspiral matched filter and recovering the time and value of the maximum of the resulting SNR time series. Although we identify regions of the parameter space in which each approximation no longer reproduces the numerical results, the approximations complement each other and together effectively cover the whole parameter space
Why is the three-nucleon force so odd?
By considering a class of diagrams which has been overlooked also in the most
recent literature on three-body forces, we extract a new contribution to the
three-nucleon interaction which specifically acts on the triplet odd states of
the two nucleon subsystem. In the static approximation, this 3N-force
contribution is fixed by the underlying 2N interaction, so in principle there
are no free parameters to adjust. The 2N amplitude however enters in the 3NF
diagram in a form which cannot be directly accessed or constrained by NN
phase-shift analysis. We conclude that this new 3N-force contribution provides
a mechanism which implies that the presence of the third nucleon modifies the
p-wave (and possibly the f-wave) components of the 2N subsystem in the
triplet-isotriplet channels.Comment: 10 Pages, 7 figures, RevTeX, twocolumn, epsf (updated version with
minor changes
Complex Conjugate Pairs in Stationary Sturmians
Sturmian eigenstates specified by stationary scattering boundary conditions
are particularly useful in contexts such as forming simple separable two
nucleon t matrices, and are determined via solution of generalised eigenvalue
equation using real and symmetric matrices. In general, the spectrum of such an
equation may contain complex eigenvalues. But to each complex eigenvalue there
is a corresponding conjugate partner. In studies using realistic
nucleon--nucleon potentials, and in certain positive energy intervals, these
complex conjugated pairs indeed appear in the Sturmian spectrum. However, as we
demonstrate herein, it is possible to recombine the complex conjugate pairs and
corresponding states into a new, sign--definite pair of real quantities with
which to effect separable expansions of the (real) nucleon--nucleon reactance
matrices.Comment: (REVTEX) 8 Pages, Padova DFPD 93/TH/78 and University of Melbourn
Practical approximation scheme for the pion dynamics in the three-nucleon system
We discuss a working approximation scheme to a recently developed formulation
of the coupled piNNN-NNN problem. The approximation scheme is based on the
physical assumption that, at low energies, the 2N-subsystem dynamics in the
elastic channel is conveniently described by the usual 2N-potential approach,
while the explicit pion dynamics describes small, correction-type effects.
Using the standard separable-expansion method, we obtain a dynamical equation
of the Alt-Grassberger-Sandhas (AGS) type. This is an important result, because
the computational techniques used for solving the normal AGS equation can also
be used to describe the pion dynamics in the 3N system once the matrix
dimension is increased by one component. We have also shown that this
approximation scheme treats the conventional 3N problem once the pion degrees
of freedom are projected out. Then the 3N system is described with an extended
AGS-type equation where the spin-off of the pion dynamics (beyond the 2N
potential) is taken into account in additional contributions to the driving
term. These new terms are shown to reproduce the diagrams leading to modern
3N-force models. We also recover two sets of irreducible diagrams that are
commonly neglected in 3N-force discussions, and conclude that these sets should
be further investigated, because a claimed cancellation is questionable.Comment: 18 pages, including 5 figures, RevTeX, Eps
Mentoring in learning development
Learning Development is still a relatively young field (Syska and Buckley, 2022), and despite a growing body of research, it remains strongly practice-oriented. This means that experience, in this case of individual Learning Developers, takes an even more central place than it does in more established fields, and sharing this experience through mentoring takes on a central role. This is why the mentoring working group has developed a Learning Development focused ALDinHE Mentoring Scheme, together with a Certified Mentor recognition that helps experienced mentors be recognised for their contribution to growing and sharing LD knowledge. This mini keynote briefly introduced the Mentoring Scheme and the CeM recognition before exploring the role mentoring can play in the professional development of Learning Developers with the audience.
The questions we asked were:
What benefits would you expect for mentees?
What benefits would you expect for mentors?
What kind of experience can be best shared through mentoring
Developing through mentoring or being mentored: ALDinHE’s new mentoring scheme and certified mentor recognition
ALDinHE is launching its new mentoring scheme and mentorship recognition to acknowledge, promote and recognise the importance of mentoring for learning development as a field that does not offer an official route into the profession. This Professional Development session introduced the mentoring scheme, explaining how to get involved, what support mentors and mentees can receive from ALDinHE and what benefits both sides can get from mentoring or being mentored. If you’re new to learning development or keen to develop more experience in a specific area with the help of a mentor, the mentoring scheme will offer you a brilliant framework to broaden your expertise. If you’re an experienced learning developer or have specific expertise you could share, find out how you could become recognised as a Certified Mentor (CeM) in learning development by ALDinHE
Isoscalar off-shell effects in threshold pion production from pd collisions
We test the presence of pion-nucleon isoscalar off-shell effects in the
reaction around the threshold region. We find that these
effects significantly modify the production cross section and that they may
provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses
psfig, updated and extended versio
Comparison between two methods of solution of coupled equations for low-energy scattering
Cross sections from low-energy neutron-nucleus scattering have been evaluated
using a coupled channel theory of scattering. Both a coordinate-space and a
momentum-space formalism of that coupled-channel theory are considered.A simple
rotational model of the channel interaction potentials is used to find results
using two relevant codes, ECIS97 and MCAS, so that they may be compared. The
very same model is then used in the MCAS approach to quantify the changes that
occur when allowance is made for effects of the Pauli principle.Comment: 6 pages, 3 figure
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