arXiv subjects

Kaanapuli Ramkumar

Publications and source records attributed to Kaanapuli Ramkumar.

6 recordsLinked to original sources

arXiv2024

Uncertainties in the Transport Properties of Helium Gas at Cryogenic Temperatures Determined Using Molecular Dynamics Simulation

In this study, the transport properties, such as diffusivity, viscosity, and thermal conductivity, of 4He at the gaseous phase are computed for state points in the temperature range of 10 K to 150 K and pressure range of 0.10 MPa (1 atm) to 0.21 MPa using classical and quantum frameworks. Within the classical molecular dynamics simulation (MDS), the Green-Kubo (GK) approach is used. The GK method has an inherent uncertainty associated with it due to the random fluctuations in the flux autocorrelation functions. Moreover, in the temperature range of 10 K to 40 K, the quantum nature of the helium gas particles becomes prominent. The classical MDS performed does not include these effects and hence introduces uncertainties in the calculated results. We discuss efficient ways of time averaging the autocorrelation function to reduce statistical fluctuations and perform the quantum scattering phase shift calculations within the Chapman-Cowling theory to study the quantum effects. Furthermore, this study also provides the transport properties data in the cryogenic temperature limit of 10 K to 150 K, which is scarcely studied in the literature and can be applied in complex systems.

physics.chem-ph↗

arXiv2024

Renormalization of Scalar and Fermion Interacting Field Theory for Arbitrary Loop: Heat-Kernel Approach

We outline a proposal, based on the Heat-Kernel method, to compute 1PI effective action up to any loop order for quantum field theory with scalar and fermion fields. We algebraically extract the divergences associated with the composite operators without explicitly performing any momentum loop integral. We perform this analysis explicitly for one and two-loop cases and pave the way for three-loop as well. Using our prescription we compute the two-loop counter terms for a theory containing higher mass dimensional effective operators that are polynomial in fields for two different cases: (i) real singlet scalar, and (ii) complex fermion-scalar interacting theories. We also discuss how the minimal Heat-Kernel fails to deal with the effective operators involving derivatives. We explicitly compute the one-loop counter terms for such a case within an $O(n)$ symmetric scalar theory employing a non-minimal Heat-Kernel. Our method computes the counter terms of the composite operators directly and is also useful for extracting infrared divergence in massless limits.

hep-th↗

arXiv2023

One-loop Effective Action up to any Mass-dimension for Non-degenerate Scalars and Fermions including Light-Heavy Mixing

We propose a Heat-Kernel-based method to compute one-loop effective action up to any mass-dimension with arbitrary numbers of non-degenerate scalars and fermions. We demonstrate our prescription by computing the dimension six effective action for arbitrary numbers of non-degenerate scalars, which are consistent with degenerate results presented in prior studies. We have further shown that the effective action for any partially degenerate mass-spectrum can be easily derived from that for the non-degenerate case by employing suitable limits for masses. Our prescription allows us to express the effective action in terms of local operators for the scenarios that involve light-heavy mixing as well, simply by employing an infrared regulator in the non-degenerate action. Along with the formalism, we have also provided the algorithm and outlined the Mathematica program to compute the result up to any mass dimension.

hep-ph↗

arXiv2023

One-loop Effective Action up to Dimension Eight: Integrating out Heavy Fermion(s)

We present the universal one-loop effective action up to dimension eight after integrating out heavy fermion(s) using the Heat-Kernel method. We have discussed how the Dirac operator being a weak elliptic operator, the fermionic operator still can be written in the form of a strong elliptic one such that the Heat-Kernel coefficients can be used to compute the fermionic effective action. This action captures the footprint of both the CP conserving as well as violating UV interactions. As it does not rely on the specific forms of either UV or low energy theories, can be applicable for a very generic action. Our result encapsulates the effects of heavy fermion loops only.

hep-ph↗

arXiv2023

One-loop Effective Action up to Dimension Eight: Integrating out Heavy Scalar(s)

We present the complete one-loop effective action up to dimension eight after integrating out degenerate scalars using the Heat-Kernel method. The result is provided without assuming any specific form of either UV or low energy theories, i.e., universal. In this paper, we consider the effects of only heavy scalar propagators in the loops. We also verify part of the results using the covariant diagram technique.

hep-ph↗

arXiv2022

A Toy Model for Low Energy Nuclear Fusion

We study the fusion of a proton with a nucleus with the emission of two photons at low incident energy of the order of eV or smaller. We use a step model for the repulsive potential between proton and the nuclei. We consider the reaction both in free space and inside a medium. We make a simple model for the medium by assuming a hard wall potential beyond a certain length scale. This essentially leads to discretization of the energy spectrum which is expected inside a medium and is seen both for a crystalline lattice structure and for amorphous materials. We use second order perturbation theory to compute the transition rate. We find that the rate in free space is very small. However in medium, the rate may be substantial. Hence, we conclude that nuclear fusion reactions may take place at low energies at observable rates.

nucl-th↗