arXiv subjects

Moutushi Dutta Choudhury

Publications and source records attributed to Moutushi Dutta Choudhury.

8 recordsLinked to original sources

arXiv2026

Yukawa scalar self energy at two loop and $\langle ϕ^2 \rangle$ in the inflationary de Sitter spacetime

We have considered the Yukawa theory at two loop in the inflationary de Sitter spacetime, for a massless minimally coupled scalar and a massless fermion. The one loop computation for the same has been investigated in detail in the earlier literatures. The chief motivation behind this study is the fact that at one loop, the scalar self energy contains only fermions, which are conformally invariant. At two loop, there are two diagrams, each containing one internal scalar line, thereby breaking the conformal invariance. This should result in the appearance of infrared secular logarithms in the scalar self energy. The renormalisation of this two loop self energy has been performed. We next compute the loop corrected coincident two point correlation function, $\langle ϕ^2\rangle$, due to the self energies. The expectation value has been taken with respect to the initial Bunch-Davies vacuum. We argue that the late time secular contribution from the local or UV self energy must dominate the non-local or IR ones in the present case, from the point of view of the powers of these large logarithms of the scale factor. This corresponds to the fact that fermion lines do not show any IR secular effect. The leading behaviour of $\langle ϕ^2\rangle$ at one and two loop are respectively found to be $\ln^3 a$ and $\ln^4 a$. These are hybrids of UV and IR logarithms, where the latter originate from the massless and minimal two external scalar lines. A resummed expression for $\langle ϕ^2\rangle$ has also been computed. The same is found to be bounded and decreasing monotonically with the increasing magnitude of the Yukawa coupling. Accordingly, the dynamically generated scalar mass increases with the increasing coupling.

hep-th↗

arXiv2024

Non-perturbative $\langle ϕ\rangle$, $\langle ϕ^2 \rangle$ and the dynamically generated scalar mass with Yukawa interaction in the inflationary de Sitter spacetime

We consider a massless minimally coupled self interacting quantum scalar field coupled to fermion via the Yukawa interaction, in the inflationary de Sitter background. The fermion is also taken to be massless and the scalar potential is taken to be a hybrid, $V(ϕ)= λϕ^4/4!+ βϕ^3/3!$ ($λ>0$). The chief physical motivation behind this choice of $V(ϕ)$ corresponds to, apart from its boundedness from below property, the fact that shape wise $V(ϕ)$ has qualitative similarity with standard inflationary classical slow roll potentials. Also, its vacuum expectation value can be negative, suggesting some screening of the inflationary cosmological constant. We choose that $\langle ϕ\rangle\sim 0$ at early times with respect to the Bunch-Davies vacuum, so that perturbation theory is valid initially. We consider the equations satisfied by $\langle ϕ(t) \rangle$ and $\langle ϕ^2(t) \rangle$, constructed from the coarse grained equation of motion for the slowly rolling $ϕ$. We then compute the vacuum diagrammes of various relevant operators using the in-in formalism up to three loop, in terms of the leading powers of the secular logarithms. For a closed fermion loop, we have restricted ourselves here to only the local contribution. These large temporal logarithms are then resummed by constructing suitable non-perturbative equations to compute $\langle ϕ\rangle$ and $\langle ϕ^2 \rangle$. $\langle ϕ\rangle$ turns out to be at least approximately an order of magnitude less compared to the minimum of the classical potential, $-3β/λ$, owing to the strong quantum fluctuations. For $\langle ϕ^2 \rangle$, we have computed the dynamically generated scalar mass at late times, by taking the appropriate purely local contributions. Variations of these quantities with respect to different couplings have also been presented.

hep-th↗

arXiv2015

Growth kinetics of NaCl crystals in a drying drop of gelatin: transition from faceted to dendritic growth

We report a study on the kinetics of drying of a droplet of aqueous gelatin containing sodium chloride. The process of drying recorded on video, clearly shows different regimes of growth leading to a variety of crystalline patterns. Large faceted crystals of $\sim$mm size form in the early stages of evaporation, followed by highly branched multi-fractal patterns with micron sized features. We simulate the growth using a simple algorithm incorporating aggregation and evaporation, which reproduces the cross-over between the two growth regimes. As evaporation proceeds, voids form in the gel film. The time development of the fluid-void system can be characterized by an Euler number. A minimum in the Euler number marks the transition between the two regimes of growth.

cond-mat.soft↗

arXiv2015

Squeeze flow of potato starch gel: effect of loading history on visco-elastic properties

In this work gelatinized potato starch is shown to retain the memory of past loading history. It exhibits a visco-elastic response which does not depend solely on instantaneous conditions. A simple squeeze flow experiment is performed, where loading is done in two steps with a time lag $τ\sim$ seconds between the steps. The effect on the strain, of varying $τ$ is reproduced by a three element visco-elastic solid model. Non-linearity is introduced through a generalized calculus approach by incorporating a non-integer order time derivative in the viscosity equation. A strain hardening proportional to the time lag between the two loading steps is also incorporated. This model reproduces the three salient features observed in the experiment, namely - the memory effect, slight initial oscillations in the strain as well as the long-time solid-like response. Dynamic visco-elasticity of the sample is also reported.

cond-mat.soft↗

arXiv2012

Aggregation Patterns of Salt Crystalizing in Drying Colloidal Solvents

We report a study of the structure of droplets of colloidal gels containing dissolved sodium chloride. The components segregate and form intricate patterns. The salt crystalizes in fractal and multi-fractal dendritic forms which are determined by the material which forms the colloidal gel. Here potato starch, gelatine and carboxymethyl cellulose have been used. The substrate also plays a role in some cases. Photographs and micrographs at different level of magnification are shown.

cond-mat.soft↗

arXiv2012

Pattern Formation in a Drying Drop of Starch Gel with Sodium Chloride

A drop of aqueous potato starch gel with a certain mole fraction of NaCl, when dried on a glass slide, exhibits strong segregation and intricate pattern formation phenomena. The salt forms radial dendritic crystalline aggregates near the centre, with the starch separating out in the form of a transparent band at the periphery. Photographs and micrographs show a series of concentric rings with different texture.

cond-mat.soft↗

arXiv2011

Spreading of Non-Newtonian and Newtonian Fluids on a Solid Substrate under Pressure

Strongly non-Newtonian fluids namely, aqueous gels of starch, are shown to exhibit visco-elastic behavior, when subjected to a load. We study arrowroot and potato starch gels. When a droplet of the fluid is sandwiched between two glass plates and compressed, the area of contact between the fluid and plates increases in an oscillatory manner. This is unlike Newtonian fluids, where the area increases monotonically in a similar situation. The periphery moreover, develops an instability, which looks similar to Saffman Taylor fingers. This is not normally seen under compression. The loading history is also found to affect the manner of spreading. We attempt to describe the non-Newtonian nature of the fluid through a visco-elastic model incorporating generalized calculus. This is shown to reproduce qualitatively the oscillatory variation in the surface strain.

cond-mat.soft↗

arXiv2010

Oscillatory Spreading and Surface Instability of a Non-Newtonian Fluid under Compression

Starch solutions, which are strongly non-Newtonian, show a surface instability, when subjected to a load. A droplet of the fluid is sandwiched between two glass plates and a weight varying from 1 to 5 kgs. is placed on the top plate. The area of contact between the fluid and plate increases in an oscillatory manner, unlike Newtonian fluids in a similar situation. The periphery moreover, develops a viscous fingering like instability, which is not expected under compression. We attempt to model the non-Newtonian nature of the fluid through a visco-elastic model incorporating generalized calculus. This is shown to exhibit a qualitatively similar oscillatory variation in the surface strain.

cond-mat.soft↗