How Long can Left and Right Handed Life Forms Coexist?

Reaction-diffusion equations based on a polymerization model are solved to simulate the spreading of hypothetic left and right handed life forms on the Earth's surface. The equations exhibit front-like behavior as is familiar from the theory of the spreading of epidemics. It is shown that the relevant time scale for achieving global homochirality is not, however, the time scale of front propagation, but the much longer global diffusion time. The process can be sped up by turbulence and large scale flows. It is speculated that, if the deep layers of the early ocean were sufficiently quiescent, there may have been the possibility of competing early life forms with opposite handedness.Comment: submitted to Int. J. Astrobiol., 15 pages, 10 figs. submitted to Int. J. Astrobiol., 15 pages, 10 fig

Electroweak Baryogenesis in a Left-Right Supersymmetric Model

The possibility of electroweak baryogenesis is considered within the framework of a left-right supersymmetric model. It is shown that for a range of parameters the large sneutrino VEV required for parity breaking varies at the electroweak phase transition leading to a production of baryons. The resulting baryon to entropy ratio is approximated to be ${n_B\over s}\sim \alpha 0.7 \times10^{-8}$, where $\alpha$ is the angle that the phase of sneutrino VEV changes at the electroweak phase transition.Comment: 9 page

Simulations of Q-Ball Formation

The fragmentation of the Affleck-Dine condensate is studied by utilizing 3+1 dimensional numerical simulations. The 3+1 dimensional simulations confirm that the fragmentation process is very similar to the results obtained by 2+1 dimensional simulations. We find, however, that the average size of Q-balls in 3+1 dimensions is somewhat larger that in 2+1 dimensions. A filament type structure in the charge density is observed during the fragmentation process. The resulting final Q-ball distribution is strongly dependent on the initial conditions of the condensate and approaches a thermal one as the energy-charge ratio of the Affleck-Dine condensate increases.Comment: 9 pages, 8 figures; corrected typos (v2,v3

Limits on Q-ball size due to gravity

Solitonic scalar field configurations are studied in a theory coupled to gravity. It is found that non-topological solitons, Q-balls, are present in the theory. Properties of gravitationally self coupled Q-balls are studied by analytical and numerical means. Analytical arguments show that, unlike in the typical flat space scenario, the size of Q-balls is ultimately limited by gravitational effects. Even though the largest Q-balls are very dense, their radii are still much larger than the corresponding Schwarzschild radii. Gravity can also act as a stabilising mechanism for otherwise energetically unstable Q-balls.Comment: 11 pages, 4 figure

Spontaneous R-Parity Violation and Electroweak Baryogenesis

The possibility of baryogenesis at the electroweak phase transition is considered within the context of a minimal supersymmetric standard model with spontaneous R-parity violation. Provided that at least one of the sneutrino fields acquires a large enough vacuum expectation value, a sufficient baryon asymmetry can be created. Compared to R-parity conserving models the choice of soft supersymmetry breaking parameters is less restricted. The observed baryon asymmetry, n_B/s ~ 10^(-10), can be explained by this scenario and the produced baryon-to-entropy ratio may easily be as high as n_B/s ~ 10^(-9).Comment: 9 pages, 1 figur

Constraints on self-interacting Q-ball dark matter

We consider different types of Q-balls as self-interacting dark matter. For the Q-balls to act as the dark matter of the universe they should not evaporate, which requires them to carry very large charges; depending on the type, the minimum charge could be as high as Q \sim 10^{33} or the Q-ball coupling to ordinary matter as small as \sim 10^{-35}. The cross-section-to-mass ratio needed for self-interacting dark matter implies a mass scale of m \sim O(1) MeV for the quanta that the Q-balls consist of, which is very difficult to achieve in the MSSM.Comment: 13 pages, 2 figure

Current Acceleration from Dilaton and Stringy Cold Dark Matter

We argue that string theory has all the ingredients to provide us with candidates for the cold dark matter and explain the current acceleration of our Universe. In any generic string compactification the dilaton plays an important role as it couples to the Standard Model and other heavy non-relativistic degrees of freedom such as the string winding modes and wrapped branes, we collectively call them stringy cold dark matter. These couplings are non-universal which results in an interesting dynamics for a rolling dilaton. Initially, its potential can track radiation and matter while beginning to dominate the dynamics recently, triggering a phase of acceleration. This scenario can be realized as long as the dilaton also couples strongly to some heavy modes. We furnish examples of such modes. We provide analytical and numerical results and compare them with the current supernovae result. This favors certain stringy candidates.Comment: 16 pages, 4 figures (colour

Q-ball collisions in the MSSM: gauge-mediated supersymmetry breaking

Collisions of non-topological solitons, Q-balls, are considered in the Minimal Supersymmetric Standard Model where supersymmetry has been broken at a low energy scale via a gauge mediated mechanism. Q-ball collisions are studied numerically on a two dimensional lattice for a range of Q-ball charges. Total cross-sections, as well as fusion and geometrical cross-sections are calculated. The total and geometrical cross-sections appear to converge with increasing charge. The fusion cross-section has been estimated to be larger than 60% of the geometrical cross-section for large balls.Comment: 9 pages, 3 figure

Cosmological solutions of braneworlds with warped and compact dimensions

We study cosmological aspects of braneworld models with a warped dimension and an arbitrary number of compact dimensions. With a stabilized radion, a number of different cosmological bulk solutions are found in a general case. Both one and two brane models are considered. The Friedmann equation is calculated in each case. Particular attention is paid to six dimensional models where we find that the usual Friedmann equation can typically be recovered without fine-tuning.Comment: 11 page