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Full-Text Articles in Physics
Caustics In Tachyon Matter And Other Born-Infeld Scalars, Gary Felder, Lev Kofman, Alexei Starobinsky
Caustics In Tachyon Matter And Other Born-Infeld Scalars, Gary Felder, Lev Kofman, Alexei Starobinsky
Physics: Faculty Publications
We consider scalar Born-Infeld type theories with arbitrary potentials V(T) of a scalar field T. We find that for models with runaway potentials V(T) the generic inhomogeneous solutions after a short transient stage can be very well approximated by the solutions of a Hamilton-Jacobi equation that describes free streaming wave front propagation. The analytic solution for this wave propagation shows the formation of caustics with multi-valued regions beyond them. We verified that these caustics appear in numerical solutions of the original scalar BI non-linear equations. Our results include the scalar BI model with …
Large Force Fluctuations In A Flowing Granular Medium, Emily Longhi, Nalini Easwar, Narayanan Menon
Large Force Fluctuations In A Flowing Granular Medium, Emily Longhi, Nalini Easwar, Narayanan Menon
Physics: Faculty Publications
We study fluctuations in the force at the boundary of a 2D granular flow. The forces are mainly impulsive at all flow rates. The probability distribution of impulses decays exponentially at large impulses, as do the forces in a static granular medium. At small impulses, the distribution evolves continuously with flow rate with no indication of the transition from collisional flow to intermittently jamming flows. However, the distribution of the time interval between collisions tends to a power law, P(τ)∼τ−3/2, showing a clear dynamical signature of the approach to jamming.
Warped Geometry Of Brane Worlds, Gary Felder, Andrei Frolov, Lev Kofman
Warped Geometry Of Brane Worlds, Gary Felder, Andrei Frolov, Lev Kofman
Physics: Faculty Publications
We study the dynamical equations for extra-dimensional dependence of a warp factor and a bulk scalar in 5D brane world scenarios with induced brane metric of constant curvature. These equations are similar to those for the time dependence of the scale factor and a scalar field in 4D cosmology, but with the sign of the scalar field potential reversed. Based on this analogy, we introduce novel methods for studying the warped geometry. We construct the full phase portraits of the warp factor/scalar system for several examples of the bulk potential. This allows us to view the global properties of the …
Cosmology With Negative Potentials, Gary Felder, Andrei Frolov, Lev Kofman, Andrei Linde
Cosmology With Negative Potentials, Gary Felder, Andrei Frolov, Lev Kofman, Andrei Linde
Physics: Faculty Publications
We investigate cosmological evolution in models where the effective potential V(f) may become negative for some values of the field f. Phase portraits of such theories in the space of variables (f,f˙ ,H) have several qualitatively new features as compared with phase portraits in the theories with V(f).0. Cosmological evolution in models with potentials with a ‘‘stable’’ minimum at V(f),0 is similar in some respects to the evolution in models with potentials unbounded from below. Instead of reaching an AdS regime dominated by the negative vacuum energy, the universe reaches a turning point where its energy density vanishes, and then …