Sharif Digital Repository

In this paper the possibility of generating large scale curvature perturbations induced from the entropic perturbations during the waterfall phase transition of the standard hybrid inflation model is studied. We show that whether or not appreciable amounts of large scale curvature perturbations are produced during the waterfall phase transition depends crucially on the competition between the classical and the quantum mechanical backreactions to terminate inflation. If one considers only the classical evolution of the system, we show that the highly blue-tilted entropy perturbations induce highly blue-tilted large scale curvature perturbations during the waterfall phase transition which... 

In this work, we study the anisotropic inflationary models. In these models, an abelian gauge field non-minimally coupled to the inflaton field plays a role in the inflation dynamicIn a gauge field,the backgroundanswer is anisotropic, in the form of metric Bianchi. In order for the model to be consistent with the observations, the level of anisotropy should be small. The anisotropy power spectrum is obtained by calculating cosmological perturbation using formalism. We show that the criticism levelled in [4] does not apply and we can repeat the calculations in the non-absorbence by calculating the anisotropy spectrum. Using the constraint on the quadrupole anisotopy, we show that the... 

According to the equivalence principal, the long wavelength perturbations must not have any dynamical effect on the short scale physics up to (k2 L/k2 s). Their effect can be always absorbed to a coordinate transformation locally. So any physical effect of such a perturbation appears only on scales larger than the scale of the perturbation. The bispectrum in the squeezed limit of the curvature perturbation in single-field slow-roll inflation is a good example, where the long wavelength effect is encoded in the spectral index through Maldacena's consistency relation. This implies that one should be able to derive the bispectrum in the squeezed limit without resorting to the in-in formalism in... 

We study the evolution of the metric perturbations in a Bianchi background in the long-wavelength limit. By applying the gradient expansion to the equations of motion we exhibit a generalized "Separate Universe" approach to the cosmological perturbation theory. Having found this consistent separate universe picture, we introduce the δ M formalism for calculating the evolution of the linear tensor perturbations in anisotropic inflation models in almost the same way that the so-called δ N formula is applied to the super-horizon dynamics of the curvature perturbations. Similar to her twin formula, δ N, this new method can substantially reduce the amount of calculations related to the evolution... 

We revisit the formation of primordial black holes (PBHs) in the radiation-dominated era for both linear and non-linear regimes, elaborating on the concept of an apparent horizon. Contrary to the expectation from vacuum models, we argue that in a cosmological setting a density fluctuation with a high density does not always collapse to a black hole. To this end, we first elaborate on the perturbation theory for spherically symmetric space times in the linear regime. Thereby, we introduce two gauges. This allows to introduce a well defined gauge-invariant quantity for the expansion of null geodesics. Using this quantity, we argue that PBHs do not form in the linear regime irrespective of the... 

We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results... 

A perturbative description of Large Scale Structure is a cornerstone of our understanding of the observed distribution of matter in the universe. Renormalization is an essential and defining step to make this description physical and predictive. Here we introduce a systematic renormalization procedure, which neatly associates counterterms to the UV-sensitive diagrams order by order, as it is commonly done in quantum field theory. As a concrete example, we renormalize the one-loop power spectrum and bispectrum of both density and velocity. In addition, we present a series of results that are valid to all orders in perturbation theory. First, we show that while systematic renormalization... 

We consider single field chaotic inflationary models plus a cosine modulation term, as in axion monodromy models, and augment them by a light scalar field with similar cosine coupling. We show that the power spectrum of curvature perturbations of this model is dominated by the one-loop contribution to the inflaton two-point function which is enhanced due to resonant interactions. This allows us to disentangle the scale of the scalar and tensor perturbations and hence, to suppress the ratio of tensor-to-scalar power spectra and alter the expression of the scalar spectral tilt from the simple chaotic models. Thus, our resonating module opens the way to reconcile chaotic models with convex... 

Expanding on [1], we analyze in detail the single field chaotic inflationary models plus a cosine modulation term, augmented by a light scalar field with inflaton dependent oscillatory mass term. We work out in detail the Feynman diagrams and compute one, two and in general estimate higher loop two and three point functions in the in-in formulation. We explicitly establish how the oscillatory mass term can amplify one-loop effects to dominate over the tree as well as the higher loop contributions. The power spectrum of curvature perturbations of this model is hence enhanced compared to the simple single field chaotic model. As a consequence, one can suppress the tensor to scalar ratio r and... 

We consider a variant of hybrid inflation where the waterfall phase transition occurs during inflation. By adjusting the parameters associated with the mass of the waterfall field, we can achieve a phase transition that is not sharp, thus inflation can proceed for about 50-60 e-folds after the waterfall phase transition. We show that one can work within the limit where the quantum back-reactions are subdominant compared to the classical back-reactions. It is shown that a significant amount of large scale curvature perturbations are induced from the entropy perturbations. The curvature perturbation spectral index is either blue or red depending on whether the mode of interest leaves the... 

This work describes a novel Fe3O4@SiO2@polypyrrole magnetic nanocomposite and its application in the preconcentration of Cd(ii) and Ni(ii) ions. The parameters affecting the preconcentration procedure were optimised by a Box-Behnken design using response surface methodology. Three variables (extraction time, magnetic sorbent amount, and pH) were selected as the main factors affecting the sorption step, while four variables (type, volume and concentration of the eluent, and elution time) were selected as the main factors in the optimisation study of the elution step. Following the sorption and elution of analytes, the ions were quantified by FAAS. The limits of detection were 0.3 and 1.2 ng... 

In this paper the tachyonic resonance preheating generated from the bosonic trilinear χ2 interactions in an expanding universe is studied. In λ 4/4 inflationary model the trilinear interaction, in contrast to the four-legs 2χ2, breaks the conformal symmetry explicitly and the resonant source term becomes nonperiodic, making the Floquet theorem inapplicable. We find that the occupation number of the produced χ particles has a nonlinear exponential growth with exponent ∼x3/2, where x is the conformal time. This should be contrasted with preheating from a periodic resonant source arising, for example, from the four-legs 2χ2 interaction, where the occupation number has a linear exponential... 

In this work we present the effective field theory of primordial statistical anisotropies generated during anisotropic inflation involving a background U(1) gauge field. Besides the usual Goldstone boson associated with the breaking of time diffeomorphism we have two additional Goldstone bosons associated with the breaking of spatial diffeomorphisms. We further identify these two new Goldstone bosons with the expected two transverse degrees of the U(1) gauge field fluctuations. Upon defining the appropriate unitary gauge, we present the most general quadratic action which respects the remnant symmetry in the unitary gauge. The interactions between various Goldstone bosons leads to... 

We present a systematic prescription for calculating cosmological correlation functions for models with derivative interactions through the wavefunction of the universe and compare this result with the "in-in"formalism - canonical approach. The key step in this procedure is to perform the path integral over conjugate momenta after which a straightforward generalisation of Feynman's Rules can be applied. We show that this integral recovers the classical action plus some additional divergent contributions which are necessary to cancel other divergences that arise due to loop diagrams involving time derivatives. As a side project, for the first time, we introduce the "off-shell"version of the... 

We try to clarify the relation of Feynman paths -which appear in the Feynman path integral formalism- with de Broglie-Bohm paths. To accomplish this, we introduce a Bohmian path integral and use it to obtain the propagator of a free particle and a general system  

We go over various view-points about wave-particle duality and criticize Schrödinger-type solution of this problem. In this framework we show that Barut's quantum theory of single events has some problems and that the non-linearization of the Schrödinger equation is of no help  

The definition of tunneling in the framework of Bohmian mechanics is used to select one of available definitions for quantum tunneling times (QTTs) within the standard interpretation as the best definition. It is demonstrated that due to experimental limitations, Bohmian mechanics leads to the same tunneling times  

Recently, people have calculated tunneling’s characteristic times within Bohmian mechanics. Contrary to some characteristic times defined within the framework of the standard interpretation of quantum mechanics, these have reasonable values. Here, we introduce one of the available definitions for tunneling’s characteristic times within the standard interpretation as the best definition that can be accepted for the tunneling times. We show that, due to experimental limitations, Bohmian mechanics leads to the same tunneling times. © 2000 The American Physical Society