118373788
DBI realizations of the pseudo-conformal universe and Galilean Genesis scenarios
The pseudo-conformal universe is an alternative to inflation in which the early universe is described by a conformal field theory on approximately flat space-time. The fields develop time-dependent expectation values, spontaneously breaking the conformal symmetries to a de Sitter subalgebra, and fields of conformal weight zero acquire a scale invariant spectrum of perturbations. In this paper, we show that the pseudo-conformal scenario can be naturally realized within theories that would ordinarily be of interest for DBI inflation, such as the world-volume theory of a probe brane in an AdS bulk space-time. In this approach, the weight zero spectator field can be associated with a geometric flat direction in the bulk, and its scale invariance is protected by a shift symmetry.
119233886
On the origin of gravitational Lorentz covariance
We provide evidence that general relativity (GR) is the unique spatially covariant effective field theory of the transverse, traceless graviton degrees of freedom. The Lorentz covariance of GR, having not been assumed in our analysis, is thus plausibly interpreted as an accidental or emergent symmetry of the gravitational sector.
7944762
Towards a Cosmological Dual to Inflation
We derive all single-field cosmologies with unit sound speed that generate scale invariant curvature perturbations on a dynamical attractor background. We identify three distinct phases: slow-roll inflation; a slowly contracting adiabatic ekpyrotic phase, described by a rapidly-varying equation of state; and a novel adiabatic ekpyrotic phase on a slowly expanding background. All of these yield identical power spectra. The degeneracy is broken at the 3-point level: unlike the nearly gaussian spectrum of slow-roll inflation, adiabatic ekpyrosis predicts large non-gaussianities on small scales.
123645883
Quark mass difference and the origin of charge symmetry breaking
Abstract Evidence for charge symmetry breaking in nuclear and particle physics is presented, and it is shown that all of the observed effects can be explained by the mass and electric charge difference between d and u quarks. While hadron masses depend on the sum of the quark masses, charge symmetry breaking effects depend on the difference between d and u quark masses, providing a new quark mass relation.
118917806
Mesons in nuclei in the light-front mean field approximation and deep-inelastic scattering
A light-front treatment for the scalar and vector meson momentum distribution functions is developed using a model in which the nucleus is treated a static source of radius $R.$ The limit $\stackrel{\ensuremath{\rightarrow}}{R}\ensuremath{\infty}$ corresponds to infinite nuclear matter. In this limit, the scalar mesons are shown to carry a vanishing momentum fraction of the nuclear plus momentum ${k}^{+},$ but the vector mesons carry a significant fraction, all occuring at the experimentally inaccessible value of ${k}^{+}=0.$ This confirms earlier work. A study of the R dependence for sizes of real nuclei shows that a fraction of the scalar and vector mesons could be observable.
118992384
Understanding the Optical Potential in HBT Interferometry
The validity of using a pion optical potential to incorporate the effects of final state interactions on HBT interferometry is investigated. We find that if the optical potential is real, the standard formalism is modified as previously described in the literature. However, if the optical potential is complex, a new term involving pion emission from eliminated states must be included. The size of such effects in previous work by Cramer and Miller is assessed.