118392481
Holographic bounds and finite inflation
We compare two holographic arguments that impose especially strong bounds on the amount of inflation. One comes from the de Sitter Equilibrium cosmology and the other from the work of Banks and Fischler. We find that simple versions of these two approaches yield the same bound on the number of e-foldings. A careful examination reveals that while these pictures are similar in spirit, they are not necessarily identical prescriptions. We apply the two pictures to specific cosmologies which expose potentially important differences and which also demonstrate ways these seemingly simple proposals can be tricky to implement in practice.
119183013
Curvature Constraints from the Causal Entropic Principle
Current cosmological observations indicate a preference for a cosmological constant that is drastically smaller than what can be explained by conventional particle physics. The causal entropic principle (Bousso et al.) provides an alternative approach to anthropic attempts to predict our observed value of the cosmological constant by calculating the entropy created within a causal diamond. We have extended this work to use the causal entropic principle to predict the preferred curvature within the 'multiverse'. We have found that values larger than {rho}{sub k}=40{rho}{sub m} are disfavored by more than 99.99% peak value at {rho}{sub {lambda}}=7.9x10{sup -123} and {rho}{sub k}=4.3{rho}{sub m} for open universes. For universes that allow only positive curvature or both positive and negative curvature, we find a correlation between curvature and dark energy that leads to an extended region of preferred values. Our universe is found to be disfavored to an extent depending on the priors on curvature. We also provide a comparison to previous anthropic constraints on open universes and discuss future directions for this work.
118407568
Chiral potentials, perturbation theory and the 1S0 channel of NN scattering
We use nucleon–nucleon phase shifts obtained from experimental data, together with the chiral expansion for the long-distance part of the NN interaction, to obtain information about the short-distance piece of the NN potential that is at work in the 1S0 channel. We find that if the scale R that defines the separation between 'long-' and 'short-' distance is chosen to be 1.8 fm then the energy dependence produced by short-distance dynamics is well approximated by a two-term polynomial for Tlab ≤ 200 MeV. We also find that a quantitative description of NN dynamics is possible, at least in this channel, if one treats the long-distance parts of the chiral NN potential in perturbation theory. However, in order to achieve this we have to choose a separation scale R that is larger than 1.0 fm.
122525865
Electroweak reactions on light nuclei in chiral perturbation theory
I discuss the calculation of electromagnetic and weak reactions in few‐nucleon systems using potentials and current operators derived within chiral effective theory (χET). Computations up to O(P3) relative to leading are considered. I first present results that show that at this order χET gives a good description of extant data on the deuteron’s charge and quadrupole form factors for momentum transfers |q|<0.6 GeV. These predictions will be challenged by forthcoming data from BLAST and JLab. I then review calculations pertaining to the χET expansion for weak currents, which has reached unprecedentedaccuracy. When used to anlayze data on the weak‐capture process, 3He(μ−,υμ)3H, it yields a tight constraint on the conserved vector‐current hypothesis.
119267197
One- and Two-Neutron Halos in Effective Field Theory
I discuss recent work our group has undertaken on effective-field-theory analyses of experimental data pertaining to one- and two-neutron halo nuclei.