4,001 research outputs found
Universality of hypercubic random surfaces
We study universality properties of the Weingarten hyper-cubic random
surfaces. Since a long time ago the model with a local restriction forbidding
surface self-bendings has been thought to be in a different universality class
from the unrestricted model defined on the full set of surfaces. We show that
both models in fact belong to the same universality class with the entropy
exponent gamma = 1/2 and differ by finite size effects which are much more
pronounced in the restricted model.Comment: 8 pages, 3 figure
Desensitizing Inflation from the Planck Scale
A new mechanism to control Planck-scale corrections to the inflationary eta
parameter is proposed. A common approach to the eta problem is to impose a
shift symmetry on the inflaton field. However, this symmetry has to remain
unbroken by Planck-scale effects, which is a rather strong requirement on
possible ultraviolet completions of the theory. In this paper, we show that the
breaking of the shift symmetry by Planck-scale corrections can be
systematically suppressed if the inflaton field interacts with a conformal
sector. The inflaton then receives an anomalous dimension in the conformal
field theory, which leads to sequestering of all dangerous high-energy
corrections. We analyze a number of models where the mechanism can be seen in
action. In our most detailed example we compute the exact anomalous dimensions
via a-maximization and show that the eta problem can be solved using only
weakly-coupled physics.Comment: 34 pages, 3 figures
Simplicial Quantum Gravity on a Computer
We describe a method of Monte-Carlo simulations of simplicial quantum gravity
coupled to matter fields. We concentrate mainly on the problem of implementing
effectively the random, dynamical triangulation and building in a
detailed-balance condition into the elementary transformations of the
triangulation. We propose a method of auto-tuning the parameters needed to
balance simulations of the canonical ensemble. This method allows us to prepare
a whole set of jobs and therefore is very useful in systematic determining the
phase diagram in two dimensional coupling space. It is of particular importance
when the jobs are run on a parallel machine.Comment: 24 pages, PostScrip
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
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