Color confinement at the boundary of the conformally compactified AdS5

The topology of closed manifolds forces interacting charges to appear in pairs. We take advantage of this property in the setting of the conformal boundary of AdS5 spacetime, topologically equivalent to the closed manifold S1× S3, by considering the coupling of two massless opposite charges on it. Taking the interaction potential as the analog of Coulomb interaction (derived from a fundamental solution of the S3 Laplace-Beltrami operator), a conformal S1× S3 metric deformation is proposed, such that free motion on the deformed metric is equivalent to motion on the round metric in the presence of the interaction potential. We give explicit expressions for the generators of the conformal algebra in the representation induced by the metric deformation.By identifying the charge as the color degree of freedom in QCD, and the two charges system as a quark-anti-quark system, we argue that the associated conformal wave operator equation could provide a realistic quantum mechanical description of the simplest QCD system, the mesons.Finally, we discuss the possibility of employing the compactification radius, R, as an- other scale along ΛQCD, by means of which, upon reparametrizing Q2c2 as (Q2c2+ħ2c2/R2), a perturbative treatment of processes in the infrared could be approached.

A fully general, non-perturbative treatment of impulsive heating

ABSTRACT Impulsive encounters between astrophysical objects are usually treated using the distant tide approximation (DTA) for which the impact parameter, b, is assumed to be significantly larger than the characteristic radii of the subject, rS, and the perturber, rP. The perturber potential is then expanded as a multipole series and truncated at the quadrupole term. When the perturber is more extended than the subject, this standard approach can be extended to the case where rS ≪ b < rP. However, for encounters with b of order rS or smaller, the DTA typically overpredicts the impulse, Δv, and hence the internal energy change of the subject, ΔEint. This is unfortunate, as these close encounters are the most interesting, potentially leading to tidal capture, mass stripping, or tidal disruption. Another drawback of the DTA is that ΔEint is proportional to the moment of inertia, which diverges unless the subject is truncated or has a density profile that falls off faster than r−5. To overcome these shortcomings, this paper presents a fully general, non-perturbative treatment of impulsive encounters which is valid for any impact parameter, and not hampered by divergence issues, thereby negating the necessity to truncate the subject. We present analytical expressions for Δv for a variety of perturber profiles, apply our formalism to both straight-path encounters and eccentric orbits, and discuss the mass-loss due to tidal shocks in gravitational encounters between equal-mass galaxies.

Maximally rotating supermassive stars at the onset of collapse: effects of gas pressure

ABSTRACT The ‘direct collapse’ scenario has emerged as a promising evolutionary track for the formation of supermassive black holes early in the Universe. In an idealized version of such a scenario, a uniformly rotating supermassive star spinning at the mass-shedding (Keplerian) limit collapses gravitationally after it reaches a critical configuration. Under the assumption that the gas is dominated by radiation pressure, this critical configuration is characterized by unique values of the dimensionless parameters J/M2 and Rp/M, where J is the angular momentum, Rp the polar radius, and M the mass. Motivated by a previous perturbative treatment, we adopt a fully non-linear approach to evaluate the effects of gas pressure on these dimensionless parameters for a large range of masses. We find that gas pressure has a significant effect on the critical configuration even for stellar masses as large as $M \simeq 10^6 \, \mathrm{M}_{\odot }$. We also calibrate two approximate treatments of the gas pressure perturbation in a comparison with the exact treatment, and find that one commonly used approximation in particular results in increasing deviations from the exact treatment as the mass decreases, and the effects of gas pressure increase. The other approximation, however, proves to be quite robust for all masses $M \gtrsim 10^4 \, \mathrm{M}_{\odot }$.

Electromagnetic decay of Monopole–Antimonopole pair

A Monopole–Antimonopole pair could annihilate producing a photon shower: Some aspects of the shower like the multiplicity distribution and angular correlations are investigated within a model suitable for processes with high multiplicities and therefore difficult to deal with standard perturbative treatment. The possible production of electron–positron pairs is also considered.