A covariant gauge-invariant three-dimensional description of relativistic bound-states

A formalism is presented which allows covariant three-dimensional bound-state equations to be derived systematically from four-dimensional ones without the use of delta-functions. The amplitude for the interaction of a bound state described by these equations with an electromagnetic probe is constructed. This amplitude is shown to be gauge invariant if the formalism is truncated at the same coupling-constant order in both the interaction kernel of the integral equation and the electromagnetic current operator.Comment: 17 pages, RevTeX, uses BoxedEPS.te

The magnetic form factor of the deuteron in chiral effective field theory

We calculate the magnetic form factor of the deuteron up to O(eP^4) in the chiral EFT expansion of the electromagnetic current operator. The two LECs which enter the two-body part of the isoscalar NN three-current operator are fit to experimental data, and the resulting values are of natural size. The O(eP^4) description of G_M agrees with data for momentum transfers Q^2 < 0.35 GeV^2.Comment: 4 pages, 2 figure

Morphological Phase Diagram for Lipid Membrane Domains with Entropic Tension

Circular domains in phase-separated lipid vesicles with symmetric leaflet composition commonly exhibit three stable morphologies: flat, dimpled, and budded. However, stable dimples (i.e., partially budded domains) present a puzzle since simple elastic theories of domain shape predict that only flat and spherical budded domains are mechanically stable in the absence of spontaneous curvature. We argue that this inconsistency arises from the failure of the constant surface tension ensemble to properly account for the effect of entropic bending fluctuations. Formulating membrane elasticity within an entropic tension ensemble, wherein tension represents the free energy cost of extracting membrane area from thermal bending of the membrane, we calculate a morphological phase diagram that contains regions of mechanical stability for each of the flat, dimpled, and budded domain morphologies

Dynamical fluctuations in biochemical reactions and cycles

We develop theory for the dynamics and fluctuations in some cyclic and linear biochemical reactions. We use the approach of maximum caliber, which computes the ensemble of paths taken by the system, given a few experimental observables. This approach may be useful for interpreting single-molecule or few-particle experiments on molecular motors, enzyme reactions, ion-channels, and phosphorylation-driven biological clocks. We consider cycles where all biochemical states are observable. Our method shows how: (1) the noise in cycles increases with cycle size and decreases with the driving force that spins the cycle and (2) provides a recipe for estimating small-number features, such as probability of backward spin in small cycles, from experimental data. The back-spin probability diminishes exponentially with the deviation from equilibrium. We believe this method may also be useful for other few-particle nonequilibrium biochemical reaction systems

Retirement Responses to Early Social Security Benefit Reductions

This paper evaluates potential responses to reductions in early Social Security retirement benefits. Using the Health and Retirement Study (HRS) linked to administrative records, we find that Social Security coverage is quite uneven in the older population: one-quarter of respondents in their late 50’s lacks coverage under the Disability Insurance program, and one-fifth lacks coverage for old-age benefits. Among those eligible for benefits, respondents who subsequently retired early appear quite similar initially to those who later filed for normal retirement benefits, but both groups were healthier and better educated than those who later filed for disability benefits. Next we investigate the potential impact of curtailing, and then eliminating, early Social Security benefits. A life-cycle model of retirement behavior provides estimated parameters used to simulate the effects of cutting early Social Security benefits on retirement pathways. We find that cutting early Social Security benefits would boost the probability of normal retirement by twice as much as it would the probability of disability retirement.

Chiral effective theory predictions for deuteron form factor ratios at low Q^2

We use chiral effective theory to predict the deuteron form factor ratio G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are calculated to next-to-next-to-leading order. At this order the chiral expansion for the NN isoscalar charge operator (including consistently calculated 1/M corrections) is a parameter-free prediction of the effective theory. Use of this operator in conjunction with NLO and NNLO chiral effective theory wave functions produces results that are consistent with extant experimental data for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance contributions to this quantity. The variation is of the same size as the discrepancy between the theoretical result and the experimental value. This motivates the renormalization of G_Q via a two-nucleon operator that couples to quadrupole photons. After that renormalization we obtain a robust prediction for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise, model-independent predictions for the values of this ratio that will be measured at the lower end of the kinematic range explored at BLAST. We also present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure