[en] Published in summary form only

[en] We investigate the evolution of cosmological perturbations in scenarios with a quintessence scalar field, both analytically and numerically. In the tracking regime for quintessence, we find the long wavelength solutions for the perturbations of the quintessence field. We discuss the possibility of isocurvature modes generated by the quintessence sector

[en] Some subtleties regarding regularizations in computing the soliton energy of degenerate systems are discussed. (author)

[en] We study the proposal to solve the coincidence problem in the non-local version of the vacuum energy sequestering mechanism by means of a scalar field in a linear potential. We show that there is no solution in the theory compatible with observations if one requires the scalar field to drive the present period of acceleration and the collapse. (paper)

[en] I give explicit formulae for full propagators of vector and scalar fields in a generic spin-1 gauge model quantized in an arbitrary linear covariant gauge. The propagators, expressed in terms of all-order one-particle-irreducible correlation functions, have a remarkably simple form because of constraints originating from Slavnov-Taylor identities of Becchi-Rouet-Stora symmetry. I also determine the behavior of the propagators in the neighborhood of the poles, and give a simple prescription for the coefficients that generalize (to the case with an arbitrary vector-scalar mixing) the standard $\sqrt{\mathcal{Z}}$ factors of Lehmann, Symanzik and Zimmermann. So obtained generalized $\sqrt{\mathcal{Z}}$ factors, are indispensable to the correct extraction of physical amplitudes from the amputated correlation functions in the presence of mixing. The standard $R_{\xi }$ gauges form a particularly important subclass of gauges considered in this paper. While the tree-level vector-scalar mixing is, by construction, absent in $R_{\xi }$ gauges, it unavoidably reappears at higher orders. Therefore the prescription for the generalized $\sqrt{\mathcal{Z}}$ factors given in this paper is directly relevant for the extraction of amplitudes in $R_{\xi }$ gauges.

[en] The free scalar field is studied on the Y-junction of three semi-infinite axes which is the simplest example of a non-manifold space. It is shown that the transition rules for this system uniquely follow from conservation of energy and charge. A discrete version of the model gives the same result

[en] In this paper we elucidate the rigid limit of N = 2 supergravity coupled to vector and hypermultiplets. In particular we show how the respective scalar field spaces reduce to their global counterparts. In the hypermultiplet sector we focus on the relation between the local and rigid c-map. (paper)

[en] We have studied the tachyon intermediate and logamediate warm inflation in loop quantum cosmological background by taking the dissipative co-efficient Γ = Γ₀ (where Γ₀ is a constant) in “intermediate” inflation and Γ = V(ϕ), (where V(ϕ) is the potential of tachyonic field) in “logamediate” inflation. We have assumed slow-roll condition to construct scalar field ϕ, potential V, N-folds, etc. Various slow-roll parameters have also been obtained. We have analyzed the stability of this model through graphical representations. (paper)

[en] A scalar field theory with a χ^†χφ interaction is known to be unstable. Yet it has been used frequently without any sign of instability in standard textbook examples and research articles. In order to reconcile these seemingly conflicting results, we show that the theory is stable if the Fock space of all intermediate states is limited to a finite number of closed χ bar χ loops associated with a field χ that appears quadradically in the interaction, and that instability arises only when intermediate states include these loops to all orders. In particular, the quenched approximation is stable

[en] The authors present a comprehensive discussion of the consistency of the effective quantum field theory of a single Z₂ symmetric scalar field. The theory is constructed from a bare Euclidean action which at a scale much greater than the particle's mass is constrained only by the most basic requirements; stability, finiteness, analyticity, naturalness, and global symmetry. They prove to all orders in perturbation theory the boundedness, convergence, and universality of the theory at low energy scales, and thus that the theory is perturbatively renormalizable in the sense that to a certain precision over a range of such scales it depends only on a finite number of parameters. They then demonstrate that the effective theory has a well-defined unitary and causal analytic S-matrix at all energy scales. They also show that redundant terms in the Lagrangian may be systematically eliminated by field redefinitions without changing the S-matrix, and discuss the extent to which effective field theory and analytic S-matrix theory are actually equivalent. All this is achieved by a systematic exploitation of Wilson's exact renormalization group flow equation, as used by Polchinski in his original proof of the renormalizability of conventional var-phi ⁴-theory. 49 refs., 4 figs