SearcharxivSearch

arXiv subjects

Amitabha Lahiri

Publications and source records attributed to Amitabha Lahiri.

At least 19 recordsLinked to original sources

Elements of Topology, Differential Geometry and General Relativity for Physicists: A Mathematica-based Tutorial Approach

This book is a self-contained, tutorial introduction to topology, differential geometry, and general relativity for students and researchers in physics. Its distinguishing feature is a Mathematica-based approach that makes abstract constructions concrete through explicit, runnable notebooks and worked examples. A key contribution is a large collection of original Mathematica notebooks, written by the authors themselves, that let readers run, verify, and extend every demonstration. The first part covers point-set topology, topological spaces, continuity of maps, homotopy, and the fundamental group with applications that highlight the role of topology in modern physics. The second and largest part develops differential geometry from the ground up: manifolds, tangent and dual spaces, vector fields, pullbacks and pushforwards, Lie brackets and Lie algebras, local flows, and the Lie derivative. It then treats tensors, differential forms, the exterior derivative, volume forms, the metric tensor, and Hodge duality, emphasizing coordinate-free formulations and their computational realization. These tools are applied to Maxwell's equations in the language of forms and the generalized Stokes theorem, while Lie groups, fiber bundles, connections, and curvature bridge geometry and gauge-theoretic physics. The final part uses this framework to present general relativity, computing curvature tensors and field equations for standard spacetimes with dedicated Mathematica packages. Throughout, the book balances mathematical rigor with hands-on computation, enabling readers both to understand the theory and to reproduce every result themselves.

math-ph

Spin-torsion interaction and geodesic bending

The intrinsic spin of fermions induces torsion in spacetime, leading to an effective four-fermion interaction. This affects the bending of null and timelike geodesics inside a star with a spherically symmetric distribution of gravitationally dense fermionic matter of constant density. Our analysis shows an additional torsional contribution to the geodesic deflection, alongside the conventional curvature-induced effect. This change depends on the fermion number density, coupling constants of the different species of fermions with different chiralities, and the temperature of the matter distribution. We have shown that the torsion-induced corrections to null geodesic bending remains very small for both low- and high-mass white dwarfs, whereas significantly larger effects may arise in more compact astrophysical objects such as neutron stars.

gr-qc

Torsional four-fermion interaction for Majorana neutrinos

Fermions generate spacetime torsion, which can be eliminated, leaving behind an effective four-fermion interaction. This term will contribute an effective mass for neutrinos propagating through matter, similar to the Wolfenstein term coming from electroweak interactions. When the neutrinos are Majorana fermions and become massive via the Type I SeeSaw mechanism, there can be additional effects due to sterile neutrinos interacting with all fermions via the torsion-induced term, as well as due to the presence of new mixing parameters. We consider different scenarios with one sterile and one or two active neutrinos -- when the torsional interaction is diagonal in the mass basis and when it is not -- and analytically find these modifications. The T violation in the 2+1 scenario is discussed for some specific mixing between the torsion fields and the mass fields.

hep-ph

Probing Geometrical NSI at the DUNE experiment

In this work, we investigate the implications of a novel non-standard interaction (NSI) of neutrinos. This interaction is geometric in origin -- it arises because the propagation of fermions in curved spacetime induces torsion. This torsion is non-propagating and can be eliminated from the action, resulting in a four-fermion interaction in a torsion-free background. The new interaction modifies the behaviour of the neutrinos passing through matter by introducing additional coupling terms, resulting in a new component in the effective potential. As a result, the neutrino oscillation probabilities in matter are altered. The relevant probabilities are computed using the Cayley-Hamilton formalism. We then numerically explore the potential to probe these torsion-induced NSI in the DUNE experiment. We obtain the bounds on the parameters characterizing the torsional effects. By selecting representative values of torsion parameters to which the DUNE experiment is sensitive, we analyse how these geometric interactions affect the experiment's sensitivity to determine neutrino mass hierarchy, the octant of the 2-3 leptonic mixing angle, and the CP phase. We also examine the new parameter degeneracies introduced by torsion effects and assess their impact on the overall sensitivities of DUNE. We find that the additional parameter degeneracies in the presence of torsion significantly affect the octant sensitivity.

hep-ph

Torsional modulation of atmospheric neutrino oscillation

Fermions act as sources of spacetime torsion. However, this torsion is non-dynamical and can be eliminated using its equations of motion. The resulting theory features an effective four-fermion interaction in a torsion-free background. Generically this interaction is non-universal and violates parity. When neutrinos propagate through matter, they experience the effect of this geometrical interaction, which is similar to the MSW effect, but diagonal in the mass basis. Since this quartic interaction term varies linearly with matter density, its effect will be more prominent for atmospheric neutrinos specially for upward going atmospheric neutrinos. We investigate the effect of spacetime geometry on $ν_μ\to ν_τ$ and $ν_μ\to ν_e$ conversion probability and $ν_μ$ survival probability, by solving the Schrödinger equation using the {Preliminary Reference Earth Model (PREM)} density profile of the Earth. We also study the dependence of atmospheric neutrino oscillation probability on the CP phase angle in presence of this effect. We further provide a discussion of the MSW and parametric resonances in presence of the geometrical interaction.

hep-ph

Effect of spacetime geometry on neutrino oscillations

Propagation of fermions in spacetime requires a spin connection, which can be split into a universal gravitational part and a non-universal ``contorsion'' part. The latter is non-dynamical and can be eliminated from the theory, leaving an effective four-fermion interaction with unknown coupling constants. The generic form of the contorsion-fermion coupling, and thus the four-fermion interaction, breaks chiral symmetry. This interaction affects all fermions -- in particular neutrinos passing through matter will notice a contribution to their effective Hamiltonian, just like the MSW effect coming from weak interactions, but diagonal in the mass basis rather than the flavor basis. Then there is a possibility that this geometrical contribution is not negligible for neutrinos passing through normal matter, provided the coupling constants are not too small. We calculate the matter potential due to this interaction and thus write the conversion and survival probabilities including its effect. We plot conversion probabilities of $ν_μ$ to $ν_e$ and $ν_τ$ for a baseline of 1300 km, as well as their dependence on the CP phase, with and without the geometrical interaction. We also plot the survival probability of reactor $\barν_e$ for different baselines.

hep-ph

Skyrmion-vortex hybrid and spin wave solutions in superconducting ferromagnets

The coexistence of Ferromagnetism and superconductivity in so called ferromagnetic superconductors is an intriguing phenomenon which may lead to novel physical effects as well as applications. Here in this work we have explored the interplay of topological excitations, namely vortices and skyrmions, in ferromagnetic superconductors using a field theoretic description of such systems. In particular, numerical solutions for the continuous spin field compatible to a given vortex profile are determined in absence and presence of a Dzyaloshinskii-Moriya interaction (DMI) term. The solutions show that the spin configuration is like a skyrmion but intertwined with the vortex structure -- the radius of the the skyrmion-like solution depends on the penetration depth and also the polarity of the skyrmion depends on the sign of the winding number. Thus our solution describes a topological structure: namely a skyrmion-vortex composite. We have also determined the spin wave solutions in such systems in presence and absence of a vortex. In absence of vortex frequency and wave vector satisfy a cubic equation which leads to various interesting features. In particular, we have shown that in the low frequency regime the minimum in dispersion relation shifts from $k=0$ to a non zero $k$ value depending on the parameters. We also discuss the nature of spin wave dispersion in the $ω\sim \Tilde{m}$ regime which shows a similar pattern in the dispersion curve. The group velocity of the spin wave would change it's sign across such a minimum which is unique to FMSC. Also, the spin wave modes around the local minimum looks like roton mode in superfluid and hence called a magnetic roton. In presence of a vortex, the spin wave amplitude is shown to vary spatially such that the profile looks like that of a Néel Skyrmion. Possible experimental signature of both solutions are also discussed.

cond-mat.supr-con

Fermion-Vortex Interactions in Axion Electrodynamics

A relativistic action for scalar condensate-fermion mixture is considered where both the scalar boson and the fermion fields are coupled to a $U(1)$ gauge field. The dynamics of the gauge field is governed by a linear combination of the Maxwell term, and the Lorentz invariant $\mathbf{E\cdot B}$ term with a constant coefficient $θ$. We obtain an effective action describing an emergent fermion-fermion interaction and fermion-vortex tube interaction by using the particle-string duality, and find that the $θ$ term can significantly affect the interaction of fermions and vortices. We also perform a dimensional reduction to show a $θ$ dependent flux attachment to the itinerant fermions.

cond-mat.supr-con

Effects of spacetime geometry on neutrino oscillation inside a Core-Collapse Supernova

Neutrinos are excellent probes of the inner structures of supernovas. However, an understanding of their dynamics remains incomplete, which is crucial for properly interpreting the detector data. The huge matter density inside a core collapse supernova affects the self-coupling of the neutrinos through a geometrical four-fermion interaction induced by spacetime torsion generated by the fermions themselves. For normal mass hierarchy, the effect is negligible; for inverted mass hierarchy however, we find that the gravitational coupling can significantly alter the flavor dynamics. The possibility of constraining the said interactions through the relative abundance of different flavors of the neutrinos is discussed.

astro-ph.HE

Exploring the Effect of Chiral Torsion on Neutrino Oscillation in Long Baseline Experiments

In curved spacetime, neutrinos experience an extra contribution to their effective Hamiltonian coming from a torsion-induced four-fermion interaction that is diagonal in mass basis and also causes neutrino mixing while propagating through fermionic matter. This geometrical quartic interaction term appears as the modification to the neutrino mass term and significantly influences both neutrino conversion and survival probabilities. Since this term varies linearly with matter density, long baseline (LBL) experiments would be a good choice to probe this effect. We put bounds on torsional coupling parameters and also see the impact of torsion on physics sensitivities in the DUNE experiment.

hep-ph

Neutrino Oscillation in Core Collapse Supernova: The Impact of Spacetime Geometry

Neutrino flavor evolution inside a core-collapse supernova is a topic of active research. The core of a supernova is an intense source of neutrinos and antineutrinos. Self-interaction among neutrinos (as well as antineutrinos) gives rise to a rich phenomenology not seen in terrestrial situations. In studies of the dynamics of flavor evolution in such environments, the gravitational effects are generally ignored. Although the curvature outside a dense core does not deviate much from a flat space, the spin of the neutrinos can still couple to the torsion of the spacetime. These extra degrees of freedom of curved spacetime have interaction strengths that are proportional to the density of the neutrinos and the other fermions \cite{Chakrabarty:2019cau} \cite{Barick:2023qjq} as well as the coupling constants of the spin-torsion interaction. We have studied the effects of such interactions in flavor evolution inside a core-collapse supernova \cite{Ghose:Manuscript}. The self-interaction gets modified by the spin-torsion interaction and the oscillation dynamics is modified. We have seen that there are noticeable changes in the flavor dynamics when the neutrino density is uniform. We have also studied the effects of such interaction in a realistic core-collapse supernova (CCSN). As neutrino astronomy enters the precision era, this study will shed light on the potential of neutrino fluxes from CCSN to probe the neutrino-neutrino interaction.

astro-ph.HE

Group Theory in Physics: An Introduction with Mathematica

Group Theory has become an invaluable tool in the physics community. Despite numerous introductory books, the subject remains challenging for beginners. Mathematica has emerged as a popular tool for research and education, offering various packages and built-in tools for Group Theory. However, these resources are often too scattered for effective educational use. This work aims to provide a comprehensive source to help beginning students grasp Group Theory concepts and their applications from a physicist's perspective, while also building familiarity with symbolic language. We present several example notebooks that succinctly cover well-known theories and demonstrate specific concepts, which can be easily adapted for educational purposes. We provide basic examples on finite, compact and non-compact groups, and motivate the use of these concepts in solving physics problems such as addition of angular momenta, modelling a system of qubits and the description of spacetime transformations.

physics.ed-ph

Cosmic Acceleration and the notion of Alternative Vacuum in Nash Theory

We argue that Nash theory, a quadratic theory of Gravity, can describe a late-time cosmic acceleration without any exotic matter or cosmological constant. The observational viability of an exact cosmological solution of Nash theory is adjudged using a Markov chain Monte Carlo simulation and JLA+OHD+BAO data sets. Departures from standard ΛCDM cosmology are noted and analyzed. We prove that the Nash vacuum dynamics is equivalent to the dynamics of an Einstein vacuum plus a self-interacting Higgs scalar field, only if a mild evolution of the Higgs Vacuum Expectation Value is allowed. This leads to variations in the mass scales of fundamental particles and the fine structure constant. The variations are found to fit nicely with the analysis of molecular absorption spectra from a series of Quasars.

gr-qc

Parity nonconservation induced by spacetime geometry

The interaction of fermion spin with spacetime can be non-universal, leading to a new interaction beyond the Standard Model, independent of gravitation. Fermions generate spacetime torsion, which can be integrated out in favor of a four-fermion interaction in a torsion-free background. This is a current-current interaction which involves all fermions and generically has different coupling constants for different chiralities and species of fermions. It does not vanish when curvature goes to zero, so accelerator experiments should be able to see its effect. We calculate the contribution of this geometrical interaction to parity nonconservation in $e^-e^-$ and $e^-D$ scattering and compare with known observations. This provides an estimate of an upper bound on the coupling constants, suggesting that the strength of the ``new physics'' can be as large as only one order of magnitude smaller than that of weak interactions.

hep-ph

Torsional four-fermion interaction and the Raychaudhuri equation

Intrinsic spin of fermions can generate torsion in spacetime. This torsion is a non-propagating field that can be integrated out, leaving an effective non-universal four-fermion interaction. This geometrical interaction affects fermions inside a matter distribution and can be expected to become stronger as the density grows. In this work, we investigate the role of this interaction in a gravitationally collapsing fermionic distribution. Our specific aim is to explore if this interaction can provide a repulsive contribution and prevent the final singularity formation. We consider a collapsing distribution of massive fermions, ignoring other interactions. Using simplified yet reasonable assumptions, we establish that a repulsive contribution can arise depending on how torsion couples with different chiralities. Also, the interaction starts to dominate as the collapse proceeds, accelerating or decelerating the collapse depending on the relative signs of the geometrical interaction between different species of fermions.

gr-qc

Neutrino oscillations induced by chiral torsion

Neutrino mixing is caused by the fact that neutrino flavors are not eigenstates of the free Hamiltonian. This causes oscillations among different neutrino flavors. When neutrinos pass through a medium, weak interactions produce different effective masses for neutrinos of different flavors, leading to a modification of the mixing parameters. In curved spacetime there is an additional contribution to neutrino Hamiltonian from a torsion-induced four-fermion interaction, which also causes neutrino mixing while propagating through fermionic matter. We provide an outline of the calculation of this effect on neutrino oscillation.

hep-ph

Neutrino oscillation caused by spacetime geometry

Effects of gravitational interaction are generally neglected in particle physics. A first order formulation of gravity is presented to include gravity in Quantum Mechanical Lagrangian of fermions. It is seen that fermions minimally coupled to gravity gives rise to a torsionless effective theory with a quartic interaction. After passing through a thermal background the most generic form of contortion contributes to neutrino effective mass. This effective mass can change the current oscillation parameters.

hep-ph

Newtonian cosmology from quantum corrected Newtonian potential

We study the Newtonian cosmology taking into account the leading classical and quantum corrections of order $\mathcal{O}(G^{2})$ in the Newtonian potential. We first derive the modified Friedmann equations starting from the non-relativistic conservation of kinetic energy and potential energy for an infinitesimal mass. We then consider the leading classical correction term and the quantum correction term in the Newtonian potential for deriving the Friedmann equation, however, the quantum correction term is too small and hence does not contribute in the physical results. We then investigate the difference in scale factor with the usual scale factor for various matter like radiation, dust and cosmological constant by considering the corrections in the Newtonian potential. We observe that the evolution of the universe is similar for radiation and dust cases at late times. The cosmological constant case shows a steep increase in the scale factor compared to the other cases. We also note that the universe may have a bounce in the case of radiation depending on the sign of the coefficient of the leading classical correction.

gr-qc