Large-scale magnetic fields, curvature fluctuations and the thermal history of the Universe

It is shown that gravitating magnetic fields affect the evolution of curvature perturbations in a way that is reminiscent of a pristine non-adiabatic pressure fluctuation. The gauge-invariant evolution of curvature perturbations is used to constrain the magnetic power spectrum. Depending on the essential features of the thermodynamic history of the Universe, the explicit derivation of the bound is modified. The theoretical uncertainty in the constraints on the magnetic energy spectrum is assessed by comparing the results obtained in the case of the conventional thermal history with the estimates stemming from less conventional (but phenomenologically allowed) post-inflationary evolutions.Comment: 21 pages, 6 included figure

Lepton Flavor Violation without Supersymmetry

We study the lepton flavor violating (LFV) processes mu -> e gamma, mu -> 3e, and mu -> e conversion in nuclei in the left-right symmetric model without supersymmetry and perform the first complete computation of the LFV branching ratios B(mu -> f) to leading non-trivial order in the ratio of left- and right-handed symmetry breaking scales. To this order, B(mu -> e gamma) and B(mu -> e) are governed by the same combination of LFV violating couplings, and their ratio is naturally of order unity. We also find B(mu -> 3 e)/B(mu -> e) \sim 100 under slightly stronger assumptions. Existing limits on the branching ratios already substantially constrain mass splittings and/or mixings in the heavy neutrino sector. When combined with future collider studies and precision electroweak measurements, improved limits on LFV processes will test the viability of low-scale, non-supersymmetric LFV scenarios.Comment: 24 pages, 7 figures, 2 table

Escape of black holes from the brane

TeV-scale gravity theories allow the possibility of producing small black holes at energies that soon will be explored at the LHC or at the Auger observatory. One of the expected signatures is the detection of Hawking radiation, that might eventually terminate if the black hole, once perturbed, leaves the brane. Here, we study how the `black hole plus brane' system evolves once the black hole is given an initial velocity, that mimics, for instance, the recoil due to the emission of a graviton. The results of our dynamical analysis show that the brane bends around the black hole, suggesting that the black hole eventually escapes into the extra dimensions once two portions of the brane come in contact and reconnect. This gives a dynamical mechanism for the creation of baby branes.Comment: 4 pages, 6 figure

Pentaquark implications for exotic mesons

If the exotic baryon $\Theta^+(1540)$ is a correlated $udud\bar{s}$ with $J^P = {1/2}^+$, then there should exist an exotic meson, $J^P = 1^-$ $\vartheta^+ (S=+2)$ $\to K^+K^0$ $\sim 1.6$GeV with width $O(10-100)$MeV. The $\pi_1(1400;1600)$ may be broad members of {\bf 10} $\pm$ \10bar in such a picture. Vector mesons in the 1.4 - 1.7GeV mass range are also compared with this picture

Macroscopic amplification of electroweak effects in molecular Bose-Einstein condensates

We investigate the possible use of Bose-Einstein condensates of diatomic molecules to measure nuclear spin-dependent parity violation effects, outlining a detection method based on the internal Josephson effect between molecular states of opposite parity. When applied to molecular condensates, the fine experimental control achieved in atomic bosonic Josephson junctions could provide data on anapole moments and neutral weak couplings.Comment: 5 pages. To be published Phys. Rev. A (Rapid Communication) (2012

Cosmological Hysteresis and the Cyclic Universe

A Universe filled with a homogeneous scalar field exhibits `Cosmological hysteresis'. Cosmological hysteresis is caused by the asymmetry in the equation of state during expansion and contraction. This asymmetry results in the formation of a hysteresis loop: $\oint pdV$, whose value can be non-vanishing during each oscillatory cycle. For flat potentials, a negative value of the hysteresis loop leads to the increase in amplitude of consecutive cycles and to a universe with older and larger successive cycles. Such a universe appears to possess an arrow of time even though entropy production is absent and all of the equations respect time-reversal symmetry ! Cosmological hysteresis appears to be widespread and exists for a large class of scalar field potentials and mechanisms for making the universe bounce. For steep potentials, the value of the hysteresis loop can be positive as well as negative. The expansion factor in this case displays quasi-periodic behaviour in which successive cycles can be both larger as well as smaller than previous ones. This quasi-regular pattern resembles the phenomenon of BEATS displayed by acoustic systems. Remarkably, the expression relating the increase/decrease in oscillatory cycles to the quantum of hysteresis appears to be model independent. The cyclic scenario is extended to spatially anisotropic models and it is shown that the anisotropy density decreases during successive cycles if the hysteresis loop is negative.Comment: 31 pages, 8 figures. Matches version published in Phys Rev D85, 123542 (2012

Burgers turbulence with pressure

The randomly driven Burgers equation with pressure is considered as a 1D model of strong turbulence of compressible fluid. It is shown that infinitely small pressure provides a finite effect on the velocity and density statistics and this case therefore is qualitatively different from turbulence without pressure. We establish the corresponding operator product expansion and predict the intermittent velocity- difference and mass-difference PDFs. We then apply the developed methods to the statistics of a passive scalar advected by the Burgers field.Comment: 4 pages, revte

Gravitational Uncertainty and Black Hole Remnants

Possible existence of black holes remnants provides a suitable candidates for dark matter. In this paper we study the possibility of existence for such remnants. We consider quantum gravitational induced corrections of black hole's entropy and temperature to investigate the possibility of such relics. Observational scheme for detection of these remnants and their cosmological constraints are discussed.Comment: 17 pages, 6 figure

Time scales separation for dynamo action

The study of dynamo action in astrophysical objects classically involves two timescales: the slow diffusive one and the fast advective one. We investigate the possibility of field amplification on an intermediate timescale associated with time dependent modulations of the flow. We consider a simple steady configuration for which dynamo action is not realised. We study the effect of time dependent perturbations of the flow. We show that some vanishing low frequency perturbations can yield exponential growth of the magnetic field on the typical time scale of oscillation. The dynamo mechanism relies here on a parametric instability associated with transient amplification by shear flows. Consequences on natural dynamos are discussed

Physical constants and the Gurzadyan-Xue formula for the dark energy

We consider cosmological implications of the formula for the dark energy density derived by Gurzadyan and Xue which predicts a value fitting the observational one. Cosmological models with varying by time physical constants, namely, speed of light and gravitational constant and/or their combinations, are considered. In one of the models, for example, vacuum energy density induces effective negative curvature, while another one has an unusual asymptotic. This analysis also explicitely rises the issue of the meaning and content of physical units and constants in cosmological context.Comment: version corrected to match the one to appear in Modern Physics Letters