S. Gautam - CAS in Physics, P. University Chandigarh, India

S. Gautam
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S. Gautam
CAS in Physics, P. University Chandigarh, India

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Nuclear Theory (20)
Mathematics - Quantum Algebra (3)
Mathematics - Representation Theory (3)
Physics - Materials Science (2)
Mathematics - Algebraic Geometry (2)
Physics - Soft Condensed Matter (1)
Physics - Strongly Correlated Electrons (1)
Mathematics - Classical Analysis and ODEs (1)
Physics - Accelerator Physics (1)
Physics - Optics (1)
Physics - Atomic and Molecular Clusters (1)
Statistics - Machine Learning (1)
Physics - Atomic Physics (1)
High Energy Physics - Experiment (1)
Computer Science - Neural and Evolutionary Computing (1)
Nuclear Experiment (1)
Physics - Instrumentation and Detectors (1)
Quantitative Biology - Neurons and Cognition (1)
Computer Science - Artificial Intelligence (1)
Computer Science - Learning (1)

Publications Authored By S. Gautam

Determining how synaptic coupling within and between regions is modulated during sensory processing is an important topic in neuroscience. Electrophysiological recordings provide detailed spiking information about neurons but have traditionally been confined to a particular region or layer of cortex. Here, we develop a novel theoretical framework that relies on efficiently calculating the first and second order statistics in a multi-population firing rate model. Read More

We study the vortex-bright solitons in a quasi-two-dimensional spin-orbit-coupled (SO-coupled) hyperfine spin-1 three-component Bose-Einstein condensate (BEC) using variational method and numerical solution of a mean-field model. The ground state of these vortex-bright solitons is radially symmetric for weak ferromagnetic and polar interactions. For a sufficiently strong ferromagnetic interaction, we observe the emergence of an asymmetric vortex-bright soliton as the ground state. Read More

Learning robust value functions given raw observations and rewards is now possible with model-free and model-based deep reinforcement learning algorithms. There is a third alternative, called Successor Representations (SR), which decomposes the value function into two components -- a reward predictor and a successor map. The successor map represents the expected future state occupancy from any given state and the reward predictor maps states to scalar rewards. Read More

We theoretically and numerically investigate the generation of fractional-charge vortex dipoles in spinor condensates with non-zero magnetization. We find that in the antiferromagnetic phase of spin-1 and spin-2 and the cyclic phase of spin-2 condensate with non-zero magnetization coupling of the density (phonon) and a spin-excitation mode results in two critical speeds for vortex-antivortex pair creation in the condensate. As a result, a Gaussian obstacle potential moving across the antiferromagnetic spin-1 or spin-2 and cyclic spin-2 spinor condensates with non-zero magnetization can lead to the creation of fractional-charge vortex dipoles. Read More

We classify all possible fractional charge vortices of charge less than unity in spin-1 and spin-2 polar and cyclic Bose-Einstein condensates (BECs) with zero magnetization. Statics and dynamics of these vortices in quasi-two-dimensional spinor BECs are studied employing accurate numerical solution and a Lagrange variational approximation. The results for density and collective-mode oscillation are illustrated using fractional-charge BEC vortex of $^{23}$Na and $^{87}$Rb atoms with realistic interaction and trapping potential parameters. Read More

We demonstrate that the ground state of a trapped spin-1 and spin-2 spinor ferromagnetic Bose-Einstein condensate (BEC) can be well approximated by a single decoupled Gross-Pitaevskii (GP) equation. Useful analytic models for the ground-state densities of ferromagnetic BECs are obtained from the Thomas-Fermi approximation (TFA) to this decoupled equation. Similarly, for the ground states of spin-1 anti-ferromagnetic and spin-2 anti-ferromagnetic and cyclic BECs, some of the spin component densities are zero which reduces the coupled GP equation to a simple reduced form. Read More

Five-component minimum-energy bound states and mobile vector solitons of a spin-orbit-coupled quasi-one-dimensional hyperfine-spin-2 Bose-Einstein condensate are studied using the numerical solution and variational approximation of a mean-field model. Two distinct types of solutions with single-peak and multi-peak density distribution of the components are identified in different domains of interaction parameters. From an analysis of Galilean invariance and time-reversal symmetry of the Hamiltonian, we establish that vector solitons with multi-peak density distribution preserve time-reversal symmetry, but cannot propagate maintaining the shape of individual components. Read More

We study the formation of bound states and three-component bright vector solitons in a quasi-one-dimensional spin-orbit-coupled hyperfine spin $f=1$ Bose-Einstein condensate using numerical solution and variational approximation of a mean-field model. In the antiferromagnetic domain, the solutions are time-reversal symmetric, and the component densities have multi-peak structure. In the ferromagnetic domain, the solutions violate time-reversal symmetry, and the component densities have single-peak structure. Read More

Authors: C. Adams, J. R. Alonso, A. M. Ankowski, J. A. Asaadi, J. Ashenfelter, S. N. Axani, K. Babu, C. Backhouse, H. R. Band, P. S. Barbeau, N. Barros, A. Bernstein, M. Betancourt, M. Bishai, E. Blucher, J. Bouffard, N. Bowden, S. Brice, C. Bryan, L. Camilleri, J. Cao, J. Carlson, R. E. Carr, A. Chatterjee, M. Chen, S. Chen, M. Chiu, E. D. Church, J. I. Collar, G. Collin, J. M. Conrad, M. R. Convery, R. L. Cooper, D. Cowen, H. Davoudiasl, A. De Gouvea, D. J. Dean, G. Deichert, F. Descamps, T. DeYoung, M. V. Diwan, Z. Djurcic, M. J. Dolinski, J. Dolph, B. Donnelly, D. A. Dwyer, S. Dytman, Y. Efremenko, L. L. Everett, A. Fava, E. Figueroa-Feliciano, B. Fleming, A. Friedland, B. K. Fujikawa, T. K. Gaisser, M. Galeazzi, D. C. Galehouse, A. Galindo-Uribarri, G. T. Garvey, S. Gautam, K. E. Gilje, M. Gonzalez-Garcia, M. C. Goodman, H. Gordon, E. Gramellini, M. P. Green, A. Guglielmi, R. W. Hackenburg, A. Hackenburg, F. Halzen, K. Han, S. Hans, D. Harris, K. M. Heeger, M. Herman, R. Hill, A. Holin, P. Huber, D. E. Jaffe, R. A. Johnson, J. Joshi, G. Karagiorgi, L. J. Kaufman, B. Kayser, S. H. Kettell, B. J. Kirby, J. R. Klein, Yu. G. Kolomensky, R. M. Kriske, C. E. Lane, T. J. Langford, A. Lankford, K. Lau, J. G. Learned, J. Ling, J. M. Link, D. Lissauer, L. Littenberg, B. R. Littlejohn, S. Lockwitz, M. Lokajicek, W. C. Louis, K. Luk, J. Lykken, W. J. Marciano, J. Maricic, D. M. Markoff, D. A. Martinez Caicedo, C. Mauger, K. Mavrokoridis, E. McCluskey, D. McKeen, R. McKeown, G. Mills, I. Mocioiu, B. Monreal, M. R. Mooney, J. G. Morfin, P. Mumm, J. Napolitano, R. Neilson, J. K. Nelson, M. Nessi, D. Norcini, F. Nova, D. R. Nygren, G. D. Orebi Gann, O. Palamara, Z. Parsa, R. Patterson, P. Paul, A. Pocar, X. Qian, J. L. Raaf, R. Rameika, G. Ranucci, H. Ray, D. Reyna, G. C. Rich, P. Rodrigues, E. Romero Romero, R. Rosero, S. D. Rountree, B. Rybolt, M. C. Sanchez, G. Santucci, D. Schmitz, K. Scholberg, D. Seckel, M. Shaevitz, R. Shrock, M. B. Smy, M. Soderberg, A. Sonzogni, A. B. Sousa, J. Spitz, J. M. St. John, J. Stewart, J. B. Strait, G. Sullivan, R. Svoboda, A. M. Szelc, R. Tayloe, M. A. Thomson, M. Toups, A. Vacheret, M. Vagins, R. G. Van de Water, R. B. Vogelaar, M. Weber, W. Weng, M. Wetstein, C. White, B. R. White, L. Whitehead, D. W. Whittington, M. J. Wilking, R. J. Wilson, P. Wilson, D. Winklehner, D. R. Winn, E. Worcester, L. Yang, M. Yeh, Z. W. Yokley, J. Yoo, B. Yu, J. Yu, C. Zhang

The US neutrino community gathered at the Workshop on the Intermediate Neutrino Program (WINP) at Brookhaven National Laboratory February 4-6, 2015 to explore opportunities in neutrino physics over the next five to ten years. Scientists from particle, astroparticle and nuclear physics participated in the workshop. The workshop examined promising opportunities for neutrino physics in the intermediate term, including possible new small to mid-scale experiments, US contributions to large experiments, upgrades to existing experiments, R&D plans and theory. Read More

We show that the third Goldstone mode in the two-species condensate mixtures, which emerges at phase-separation, gets hardened when the confining potentials have separated trap centers. The {\em sandwich} type condensate density profiles, in this case, acquire a {\em side-by-side} density profile configuration. We use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution and density profiles for these phase transitions at $T=0$. Read More

We study the ground-state density profile of a spin-orbit coupled $f=2$ spinor condensate in a quasi-one-dimensional trap. The Hamiltonian of the system is invariant under time reversal but not under parity. We identify different parity- and time-reversal-symmetry-breaking states. Read More

We study a spin-orbit (SO) coupled hyperfine spin-1 Bose-Einstein condensate (BEC) in a quasi-one-dimensional trap. For a SO-coupled BEC in a one-dimensional box, we show that in the absence of the Rabi term, any non-zero value of SO coupling will result in a phase separation among the components for a ferromagnetic BEC, like $^{87}$Rb. On the other hand, SO coupling favors miscibility in a polar BEC, like $^{23}$Na. Read More

Vortex reconnections plays an important role in the turbulent flows associated with the superfluids. To understand the dynamics, we examine the reconnections of vortex rings in the superfluids of dilute atomic gases confined in trapping potentials using Gross-Petaevskii equation. Furthermore we study the reconnection dynamics of coreless vortex rings, where one of the species can act as a tracer. Read More

We study the dynamics of a single and a corotating vortex pair in a dipolar Bose-Einstein condensate in the framework of dissipative Gross-Pitaevskii equation. This simple model enables us to simulate the effect of finite temperature on the vortex dynamics. We study the effect of dipolar interactions on the dynamics of a single vortex in the presence of phenomenological dissipation. Read More

Let ${\mathfrak g}$ be a complex semisimple Lie algebra, and $Y_h({\mathfrak g})$, $U_q(L{\mathfrak g})$ the corresponding Yangian and quantum loop algebra, with deformation parameters related by $q=\exp(\pi i h)$. When $h$ is not a rational number, we constructed in arXiv:1310.7318 a faithful functor $\Gamma$ from the category of finite-dimensional representations of $Y_h ({\mathfrak g})$ to those of $U_q(L{\mathfrak g})$. Read More

We study the merging and splitting of quasi-two-dimensional Bose-Einstein condensates with strong dipolar interactions. We observe that if the dipoles have a non-zero component in the plane of the condensate, the dynamics of merging or splitting along two orthogonal directions, parallel and perpendicular to the projection of dipoles on the plane of the condensate are different. The anisotropic merging and splitting of the condensate is a manifestation of the anisotropy of the roton-like mode in the dipolar system. Read More

Let g be a complex, semisimple Lie algebra, and Y_h(g) and U_q(Lg) the Yangian and quantum loop algebra of g. Assuming that h is not a rational number and that q=exp(i \pi h), we construct an equivalence between the finite-dimensional representations of U_q(Lg) and an explicit subcategory of those of Y_h(g) defined by choosing a branch of the logarithm. This equivalence is governed by the monodromy of the abelian additive difference equations defined by the commuting fields of Y_h(g). Read More

We study the dynamics of a single and a pair of vortices in quasi two-dimensional Bose-Einstein condensates at finite temperatures. We use the stochastic Gross-Pitaevskii equation, which is the Langevin equation for the Bose-Einstein condensate, to this end. For a pair of vortices, we study the dynamics of both the vortex-vortex and vortex-antivortex pairs, which are generated by rotating the trap and moving the Gaussian obstacle potential, respectively. Read More

We show that the third Goldstone mode, which emerges in binary condensates at phase-separation, persists to higher inter-species interaction for density profiles where one component is surrounded on both sides by the other component. This is not the case with symmetry-broken density profiles where one species is to entirely to the left and the other is entirely to the right. We, then, use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution at $T\neq0$ and demonstrate the existence of mode bifurcation near the critical temperature. Read More

Present work investigates the magnetic and electronic structure of MgO/Fe/MgO/Fe/Co/Au multilayer stack grown on Si(100) substrates by electron beam evaporation method. X-ray diffraction study depicts polycrystalline nature of the multilayers. Results obtained from vibrating sample magnetometry (VSM) and near-edge X-ray absorption fine structure spectra (NEXAFS) at Fe & Co L- and Mg & O K-edges are applied to understand the magnetic and electronic properties of this stack and its interface properties. Read More

We examine the generation and subsequent evolution of Rayleigh Taylor instability in anisotropic binary Bose-Einstein condensates. Considering a pancake-shaped geometry, to initiate the instability we tune the intraspecies interaction and analytically study the normal modes of the interface in elliptic cylindrical coordinates. The normal modes are then Mathieu functions and undergoes bifurcation at particular values of anisotropy and ratio of number of atoms. Read More

We investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant non-linear Schr\"odinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex-antivortex pair into multiple vortex rings and ultimately into sound waves. Read More

We theoretically investigate the generation of the vortex dipoles in superfluid Fermi gas in the BCS limit. The vortex dipoles are generated in superfluid either by moving an obstacle above a critical speed or due to the decay of the shock waves obtained on the sudden mixing of two superfluid fragments. We observe that in pancake-shaped traps, the shock waves can lead to the formation of density ripples, which decay into vortex dipoles due to the onset of snake instability. Read More

We provide a general scheme for proving $L^p$ estimates for certain bilinear Fourier restrictions outside the locally $L^2$ setting. As an application, we show how such estimates follow for the lacunary polygon. In contrast with prior approaches, our argument avoids any use of the Rubio de Francia Littlewood--Paley inequality. Read More

The effects of 200-MeV Ag^{+15} ion irradiation on the optical properties of TiO_{2} and SnO_{2} thin films prepared by using the RF magnetron sputtering technique were investigated. These films were characterized by using UV-vis spectroscopy, and with increasing irradiation fluence, the transmittance for the TiO_{2} films was observed to increase systematically while that for SnO_{2} was observed to decrease. Absorption spectra of the irradiated samples showed minor changes in the indirect bandgap from 3. Read More

In the present work, we make confrontation of our theoretical calculations using quantum molecular dynamics model with the experimental data for the reactions of $^{40}Ar$ +$^{45}$Sc, $^{197}Au$ +$^{197}$Au and $^{129}Xe$ +$^{119}$Sn at different incident energies. In these reactions, we display the charge distribution and energy dependence of fragments multiplicity. Our results indicate good agreement with the experimental data for all the reactions. Read More

We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilation events numerically and observe that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the coherence length. Read More

We study the motion of the Gaussian obstacle potential created by blue detuned laser beam through a phase-separated binary condensate in pancake-shaped traps. For the velocity of the obstacle above a critical velocity, we observe the generation of vortex dipoles in the outer component which can penetrate the inner component. This is equivalent to finite, although small, transport of outer component across the inner component. Read More

We show that the monodromy of the trigonometric Casimir connection on the tensor product of evaluation modules of the Yangian Ysl_2 is described by the quantum Weyl group operators of the quantum loop algebra U_h(Lsl_2). The proof is patterned on the second author's computation of the monodromy of the rational Casimir connection for sl_n via the dual pair (gl_k,gl_n), and rests ultimately on the Etingof-Geer-Schiffmann computation of the monodromy of the trigonometric KZ connection. It relies on two new ingredients: an affine extension of the duality between the R-matrix of U_h(sl_k) and the quantum Weyl group element of U_h(sl_2), and a formula expressing the quantum Weyl group action of the coroot lattice of SL_2 in terms of the commuting generators of U_h(Lsl_2). Read More

We study the sensitivity of isospin dependence of nucleon-nucleon cross section and symmetry energy on the collective transverse in-plane flow. We find that collective transverse flow in Ca+Ca reactions shows great sensitivity to isospin dependence of nn cross section and symmetry energy. Read More

We study the behavior of participant and spectator matter and thermalization in neutron rich systems at the energy of vanishing flow. Our study indicates that participant-spectator matter follows a similar behavior for neutron-rich systems and for systems lie on the stability line. Read More

We study the role of colliding geometry on the N/Z dependence of balance energy using isospin-dependent quantum molecular dynamics model. Our study reveals that the N/Z dependence of balance energy becomes much steeper for peripheral collisions as compared to the central collisions. We also study the effect of system mass on the impact parameter dependence of N/Z dependence of balance energy. Read More

Effect of momentum-dependent interactions and broader Gaussian is investigated on the emission of various fragments formed in a heavy-ion reaction. We also study the corresponding structure details of those fragments for broader Gaussian and momentum-dependent interactions. We find that nucleons forming the fragments belong to same region of the phase space Read More

We study the N/Z dependence of balance energy throughout the mass range for colliding geometry varying from central to peripheral ones. Our results indicate that balance energy decreases linearly with increase in N/Z ratio for all the masses throughout the colliding geometry range. Also, the N/Z dependence of balance energy is sensitive to symmetry energy. Read More

We study the sensitivity of transverse flow towards the different density dependence of symmetry energy in Fermi energy region. Our results show that transverse flow shows sensitivity to different density dependence of symmetry energy. The mechanism for sensitivity towards different density dependence of symmetry energy is also discussed. Read More

We study nuclear dynamics at the energy of vanishing flow of neutron-rich systems having N/Z ratio 1.0, 1.6 and 2. Read More

We study the N/Z dependence of participant-spectator matter for Ca+Ca reactions at 50 and 250MeV/nucleon. We also study the role of symmetry energy and momentum-dependent interactions on the N/Z dependence of participant-spectator matter. Read More

We study the transverse flow for systems having various N/Z ratios. We find the transverse flow is sensitive to N/Z ratio and, in fact, increases with N/Z of the system. The relative contribution of symmetry energy and isospin dependence of nucleon-nucleon cross section is also investigated. Read More

We study the participant-spectator matter at the energy of vanishing flow for neutron-rich systems. Our study reveals similar behaviour of articipant-spectator for neutron-rich systems as for stable systems and also points towards nearly mass independence behaviour of participant-spectator matter for neutron-rich systems at the energy of vanishing flow. We also study the thermalization reached in the reactions of neutron-rich systems. Read More

We show that quasi-one dimensional Bose-Einstein condensate under suitable conditions can exhibit a Berezinskii-Kosterlitz-Thouless phase transition. The role played by quantized vortices in two dimensional case, is played in this case by dark solitons. We find that the critical temperature for this transition lies in nano Kelvin range and below, for a wide range of experimentally accessible parameters. Read More

The role of momentum correlations in fragmentation is studied within the framework of quantum molecular dynamics model. Our study is carried out by imposing momentum cut in the clusterization algorithm. The study reveals a strong effect of momentum cut in the fragmentation pattern. Read More

Vortex dipoles are generated when an obstacle moves through a superfluid. In case of phase-separated binary condensates, with appropriate interaction parameters in pan-cake shaped traps, we show that coreless vortex dipoles are created when a Gaussian obstacle beam traverses across them above a critical speed. As the obstacle passes through the inner component, it carries along a bubble of the outer component. Read More

We study the participant-spectator matter, density and temperature reached in heavy-ion reactions of neutron-rich systems having N/Z varying from 1.0 to 2.0 at 50 and 250 MeV/nucleon. Read More

We study nuclear dynamics at the the energy of vanishing flow for neutron-rich systems. In particular, we shall study the collision rate, density and temperature reached in a heavy-ion reaction with neutron-rich systems. We shall also study the mass dependence of these quantities. Read More

We study the sensitivity of the collective transverse in-plane flow to the symmetry energy and its density dependence at Fermi energies and higher incident energies. We find that collective transverse in-plane flow is sensitive to the symmetry energy and its density dependence at Fermi energies whereas it shows insensitivity at higher incident energies. Read More

We study the N/Z dependence of energy of vanishing flow or balance energy for different isotopic series of various system masses like Ca+Ca, Ni+Ni, Zr+Zr, Sn+Sn and Xe+Xe. We find that balance energy decreases with N/Z of the system and follows a linear behaviour. The slope of N/Z dependence is steeper for lighter systems like Ca+Ca and less for heavier ones like Xe+Xe. Read More

We study the relative contribution of the symmetry energy and isospin dependence of the nucleon-nucleon cross section to the collective transverse in-plane flow for the reactions of Ca+Ca having N/Z varying from 1.0, 1.6 and 2. Read More

We study the system size dependence of the participant and spectator matter at the energy of vanishing flow for systems having N/Z ratios as 1.0, 1.6 and 2. Read More

The role of momentum correlations is studied in the properties of light and medium mass fragments by imposing momentum cut in clustering the phase space. Our detailed investigation shows that momentum cut has major role to play in the properties of fragments. Read More

The role of momentum correlations is studied in the production of light and medium mass fragments by imposing momentum cut in clusterization the phase space. Our detailed investigation shows that momentum cut has major role to play in the emission of fragments. Read More