arXiv subjects

Gaurav Tomar

Publications and source records attributed to Gaurav Tomar.

At least 37 records · Page 2Linked to original sources

arXiv2023

Diffusion dynamics of star-shaped macromolecules in dilute solutions

Polymer chains dissolved in a solvent take random conformations due to large internal degrees of freedom and are characterized geometrically by their average shape and size. The diffusive dynamics of such large macromolecules play an indispensable role in a plethora of engineering applications. The influence of the size of the polymer chain on its diffusion is well studied, whereas the same cannot be said for the shape of the polymer chain. In the present work, the influence of shape on the center-of-mass diffusion of the star-shaped chains in solution is investigated using Multi-particle Collision Dynamics. Star-shaped chains of varying degrees of functionality are modeled in a good solvent at infinite dilution. The radius of gyration($R_g$) of the star-shaped chains follows a functionality-independent scaling law with the chain length($N$), $R_g \sim N^ν$, where $ν\sim 0.627$. The shape of the polymer chains is calibrated by relative shape anisotropy. Highly anisotropic star-shaped polymer chains are found to have a faster rate of diffusion along the translational direction due to a slower rate of rotational diffusion when the radius of gyration of the polymer chains is maintained constant.

cond-mat.soft↗

arXiv2023

Probing Non-Standard Neutrino Interactions with Interference: Insights from Dark Matter and Neutrino Experiments

Neutrino-electron scattering experiments play a crucial role in investigating the non-standard interactions of neutrinos. In certain models, these interactions can include interference terms that may affect measurements. Next-generation direct detection experiments, designed primarily for dark-matter searches, are also getting sensitive to probe the neutrino properties. We utilise the data from XENONnT, a direct detection experiment, and Borexino, a low-energy solar neutrino experiment, to investigate the impact of interference on non-standard interactions. Our study considers models with an additional $U(1)$, including $U(1)_{B-L}$, $U(1)_{L_e-L_μ}$, and $U(1)_{L_e-L_τ}$, to investigate the impact of interference on non-standard neutrino interactions. We demonstrate that this interference can lead to a transition between the considered non-standard interaction models in the energy range relevant to both the XENONnT and Borexino experiments. This transition can be used to distinguish among the considered models if any signals are observed at direct detection or neutrino experiments. Our findings underscore the importance of accounting for the interference and incorporating both direct detection and solar neutrino experiments to gain a better understanding of neutrino interactions and properties.

hep-ph↗

arXiv2023

Low-mass extension of direct detection bounds on WIMP-quark and WIMP-gluon effective interactions using the Migdal effect

Updating a previous analysis where we used elastic nuclear recoils we study the Migdal effect to extend to low WIMP masses the direct detection bounds to operators up to dimension 7 of the relativistic effective field theory describing WIMP interactions with quarks and gluons. To this aim we include in our analysis the data of the XENON1T, SuperCDMS, COSINE-100, and DarkSide-50 experiments and assume a standard Maxwellian for the WIMP velocity distribution. We find that the bounds can reach down to a WIMP mass $\simeq$20 MeV, although in the case of higher-dimension operators the energy scale of the ensuing constraints may be inconsistent with the validity of the effective theory.

hep-ph↗

arXiv2022

Linear stability analysis of particle-laden planar jet in the dilute suspension limit

Particle laden flows are commonly seen in many industrial applications such as fluidized beds in process industry, air laden with abrasive particles in abrasive machining and particle laden plumes in chemical industries. In the present work, we perform local analysis of a particle laden planar jet in the dilute suspension regime. Unladen parallel planar jets have been extensive studied using normal modes and is shown to have two unstable modes namely sinuous and varicose modes. Sinuous modes are found to be more unstable compared to the varicose modes. In the present study, we investigate the effect of particles on the stability of planar jets. Addition of particles at low Stokes numbers (St) (fine particles) results in higher growth rates than that of the unladen jet. In the intermediate Stokes number regime, addition of particles have a stabilizing effect on both the sinuous and the varicose modes. Interestingly for St~10, the unstable varicose mode is completely damped. Increasing the Stokes number by increasing the particle size, both sinuous and varicose modes show increasing growth rates, while increasing density ratio has a stabilizing effect on the flow. For non uniform particle loading, additional modes apart from the sinuous and varicose modes are observed. These modes suggests occurrence of compositional instability with an increased particle accumulation in the shear layer that is an order of magnitude higher compared to that of the sinuous and varicose modes.

physics.flu-dyn↗

arXiv2022

Complementarity of experiments in probing the non-relativistic effective theory of dark matter-nucleon interactions

The non-relativistic effective theory of dark matter-nucleon interactions depends on 28 coupling strengths for dark matter spin up to 1/2. Due to the vast parameter space of the effective theory, most experiments searching for dark matter interpret the results assuming that only one of the coupling strengths is non-zero. On the other hand, dark matter models generically lead in the non-relativistic limit to several interactions which interfere with one another, therefore the published limits cannot be straightforwardly applied to model predictions. We present a method to determine a rigorous upper limit on the dark matter-nucleon interaction strength including all possible interferences among operators. We illustrate the method to derive model independent upper limits on the interaction strengths from the null search results from XENON1T, PICO-60 and IceCube. For some interactions, the limits on the coupling strengths are relaxed by more than one order of magnitude. We also present a method that allows to combine the results from different experiments, thus exploiting the synergy between different targets in exploring the parameter space of dark matter-nucleon interactions.

hep-ph↗

arXiv2021

WimPyDD: an object-oriented Python code for WIMP-nucleus scattering direct detection in virtually any scenario

We introduce WimPyDD, a modular, object-oriented and customisable Python code that accurately predicts the expected WIMP-nucleus scattering rates in WIMP direct-detection experiments including the response of the detector. WimPyDD utilises the framework of Galilean-invariant non-relativistic effective theory, allowing to handle an arbitrary number of effective operators, and can perform the calculation of the excepted rate in virtually any scenario, including inelastic scattering, WIMPs with an arbitrary spin, and a generic velocity distribution in the Galactic halo. The power and flexibility of WimPyDD is discussed in some explicit examples.

hep-ph↗

arXiv2021

WimPyDD: an object-oriented Python code for the calculation of WIMP direct detection signals

We introduce WimPyDD, a modular, object-oriented and customizable Python code that calculates accurate predictions for the expected rates in Weakly Interacting Massive Particle (WIMP) direct-detection experiments within the framework of Galilean-invariant non-relativistic effective theory in virtually any scenario, including inelastic scattering, an arbitrary WIMP spin and a generic WIMP velocity distribution in the Galactic halo. WimPyDD exploits the factorization of the three main components that enter in the calculation of direct detection signals: i) the Wilson coefficients that encode the dependence of the signals on the ultraviolet completion of the effective theory; ii) a response function that depends on the nuclear physics and on the main features of the experimental detector (acceptance, energy resolution, response to nuclear recoils); iii) a halo function that depends on the WIMP velocity distribution and that encodes the astrophysical inputs. In WimPyDD these three components are calculated and stored separately for later interpolation and combined together only as the last step of the signal evaluation procedure. This makes the phenomenological study of the direct detection scattering rate with WimPyDD transparent and fast also when the parameter space of the WIMP model has a large dimensionality.

hep-ph↗

arXiv2021

The phenomenology of nuclear scattering for a WIMP of arbitrary spin

We provide a first systematic and quantitative discussion of the phenomenology of the non-relativistic effective Hamiltonian describing the nuclear scattering process for a Weakly Interacting Massive Particle (WIMP) of arbitrary spin $j_χ$. To this aim we obtain constraints from a representative sample of present direct detection experiments assuming the WIMP-nucleus scattering process to be driven by each one of the 44 effective couplings that arise for $j_χ\le$ 2. We find that a high value of the multipolarity $s\le 2 j_χ$ of the coupling, related to the power of the momentum transfer $q$ appearing in the scattering amplitude, leads to a suppression of the expected rates and pushes the expected differential spectra to large recoil energies $E_R$. For $s\le$ 4 the effective scales probed by direct detection experiments can be suppressed by up to 5 orders of magnitude compared to the case of a standard spin-independent interaction. For operators with large $s$ the expected differential spectra can be pushed to recoil energies in the MeV range, with the largest part of the signal concentrated at $E_R\gtrsim$ 100 keV and a peculiar structure of peaks and minima arising when both the nuclear target and the WIMP are heavy. As a consequence the present bounds on the effective operators can be significantly improved by extending the recoil energy intervals to higher recoil energies. Our analysis assumes effective interaction operators that are irreducible under the rotation group. Such operators drive the interactions of high-multipole dark matter candidates, i.e. states that possess only the highest multipole allowed by their spin. As a consequence our analysis represents also the first phenomenological study of the direct detection of quadrupolar, octupolar, and hexadecapolar dark matter.

hep-ph↗

arXiv2021

Interface reconstruction and advection schemes for volume of fluid method in axisymmetric coordinates

Volume of fluid(VOF) method is a sharp interface method employed for simulations of two phase flows. Interface in VOF is usually represented using piecewise linear line segments in each computational grid based on the volume fraction field. While VOF for cartesian coordinates conserve mass exactly, existing algorithms do not show machine-precision mass conservation for axisymmetric coordinate systems. In this work, we propose analytic formulae for interface reconstruction in axisymmetric coordinates, similar to those proposed by Scardovelli and Zaleski (J. Comput. Phys. 2000) for cartesian coordinates. We also propose modifications to the existing advection schemes in VOF for axisymmetric coordinates to obtain higher accuracy in mass conservation

physics.comp-ph↗

arXiv2020

The effective theory of nuclear scattering for a WIMP of arbitrary spin

We introduce a systematic approach to characterize the most general non-relativistic WIMP-nucleus interaction allowed by Galilean invariance for a WIMP of arbitrary spin $j_χ$ in the approximation of one-nucleon currents. Five nucleon currents arise from the nonrelativistic limit of the free nucleon Dirac bilinears. Our procedure consists in (1) organizing the WIMP currents according to the rank of the $2 j_χ+1$ irreducible operator products of up to $2 j_χ$ WIMP spin vectors, and (2) coupling each of the WIMP currents to each of the five nucleon currents. The transferred momentum $q$ appears to a power fixed by rotational invariance. For a WIMP of spin $j_χ$ we find a basis of 4+20$j_χ$ independent operators that exhaust all the possible operators that drive elastic WIMP-nucleus scattering in the approximation of one-nucleon currents. By comparing our operator basis, which is complete, to the operators already introduced in the literature we show that some of the latter for $j_χ=1$ were not independent and some were missing. We provide explicit formulas for the squared scattering amplitudes in terms of the nuclear response functions, which are available in the literature for most of the targets used in WIMP direct detection experiments.

hep-ph↗

arXiv2020

Connecting ANITA Anomalous Events to a Non-thermal Dark Matter Scenario

The ANtarctic Impulsive Transient Antenna (ANITA) collaboration has observed two EeV-energy, upward going events originating from below the horizon. As no standard model (SM) particles, propagating through the earth at such energy and exit angles, can give rise to the required survival probability for the observed events, several beyond standard model (BSM) proposals have come up. We propose a scenario where a $Z_2$ odd sector is responsible for such anomalous events. The next to lightest $Z_2$ odd particle or the next to lightest stable particle (NLSP), created from ultra high energy neutrino interactions with nucleons, can pass through the earth and then decay into the lightest $Z_2$ odd particle or the lightest stable particle (LSP) and a tau lepton. The long-lived nature of the NLSP requires its coupling with the LSP to be very small, keeping the LSP out of thermal equilibrium in the early universe. The LSP can then be a non-thermal dark matter while the tau leptons produced from NLSP decay after passing through the earth can explain the ANITA events. We first show that a purely non-thermal dark matter scenario can not give rise to the required event rates while a hybrid scenario where dark matter can have both thermal as a well non-thermal contribution to its relic abundance, serves the purpose.

hep-ph↗

arXiv2020

Detailed numerical simulations of atomization of a liquid jet in a swirling gas crossflow

Breakup of a liquid jet in a high speed gaseous crossflow finds wide range of engineering and technological applications, especially in the combustors of the gas turbine engines in aerospace industry. In this study, we present volume-of-fluid method based direct numerical simulations of a liquid jet injected into a swirling crossflow of gas. The liquid is injected radially outwards from a central tube to a confined annular space with a swirling gas crossflow. The essential features of the jet breakup involving jet flattening, surface waves and stripping of droplets from the edges of the jet are captured in the simulations. We discuss the effect of swirl on the spray characteristics such as jet trajectory, column breakup-length, and size, shape-factor and velocity distribution of the drops. Drop size increases with swirl and penetration is slightly reduced. Moreover, the trajectory follows an angle (azimuthal) that is smaller than the geometric angle of the swirl at the inlet. Interestingly, we also observe coalescence events downstream of the jet that affect the final droplet size distribution for the geometry considered in this study.

physics.flu-dyn↗

arXiv2019

Is a WIMP explanation of the DAMA modulation effect still viable?

We show that the weakly interacting massive particle (WIMP) scenario of proton-philic spin-dependent inelastic dark matter can still provide a viable explanation of the observed DAMA effect in compliance with the constraints from other experiments. We also show that, although the COSINE-100 collaboration has recently tested the DAMA effect using the same target material, for the time being the comparison between DAMA and COSINE-100 still depends on the particle-physics model.

hep-ph↗

arXiv2019

A DAMA/Libra-phase2 analysis in terms of WIMP-quark and WIMP-gluon effective interactions up to dimension seven

We analyze the DAMA/Libra-phase2 modulation result using a basis of 16 effective operators describing the WIMP interaction with photons, gluons and quarks up to mass dimension seven. For each operator we fix the effective theory at the scale of 2 GeV and parametrize WIMP-quark interactions in terms of two independent couplings for up-type and down-type quarks. We discuss the connection with the non-relativistic limit of the effective theory in terms of operators invariant by Galilean transformations, and the impact of the ensuing momentum-dependent Wilson coefficients due to long-range interactions or light meson poles. Most relativistic operators yield a good fit of the DAMA modulation effect, although for parameters excluded by the constraints from XENON1T and PICO60.

hep-ph↗

arXiv2019

On the sensitivity of present direct detection experiments to WIMP-quark and WIMP-gluon effective interactions: a systematic assessment and new model-independent approaches

Assuming for Weakly Interacting Massive Particles (WIMPs) a Maxwellian velocity distribution in the Galaxy we provide an assessment of the sensitivity of existing Dark Matter (DM) direct detection (DD) experiments to operators up to dimension 7 of the relativistic effective field theory describing dark matter interactions with quarks and gluons . In particular we focus on a systematic approach, including an extensive set of experiments and large number of couplings, both exceeding for completeness similar analyses in the literature. The relativistic effective theory requires to fix one coupling for each quark flavor, so in principle for each different combination the bounds should be recalculated starting from direct detection experimental data. To address this problem we propose an approximate model-independent procedure that allows to directly calculate the bounds for any combination of couplings in terms of model-independent limits on the Wilson coefficients of the non-relativistic theory expressed in terms of the WIMP mass and of the neutron-to-proton coupling ratio $c^n/c^p$. We test the result of the approximate procedure against that of a full calculation, and discuss its possible pitfalls and limitations. We also provide a simple interpolating interface in Python that allows to apply our method quantitatively.

hep-ph↗

arXiv2019

COSINE-100 and DAMA/LIBRA-phase2 in WIMP effective models

Assuming a standard Maxwellian for the WIMP velocity distribution, we obtain the bounds from null WIMP search results of 59.5 days of COSINE-100 data on the DAMA/LIBRA-phase2 modulation effect within the context of the non-relativistic effective theory of WIMP-nucleus scattering. Here, we systematically assume that one of the effective operators allowed by Galilean invariance dominates in the effective Hamiltonian of a spin-1/2 dark matter (DM) particle. We find that, although DAMA/LIBRA and COSINE-100 use the same sodium-iodide target, the comparison of the two results still depends on the particle-physics model. This is mainly due to two reasons: i) the WIMP signal spectral shape; ii) the expected modulation fractions, when the upper bound on the time-averaged rate in COSINE-100 is converted into a constraint on the annual modulation component in DAMA/LIBRA. We find that the latter effect is the dominant one. For several effective operators the expected modulation fractions are larger than in the standard spin-independent or spin-dependent interaction cases. As a consequence, compatibility between the modulation effect observed in DAMA/LIBRA and the null result from COSINE-100 is still possible for several non-relativistic operators. At low WIMP masses such relatively high values of the modulation fractions arise because COSINE-100 is mainly sensitive to WIMP-sodium scattering events, due to the higher threshold compared to DAMA/LIBRA. A next COSINE analysis is expected to have a full sensitivity for the 5$σ$ region of DAMA/LIBRA.

hep-ph↗

arXiv2019

Probing DAMA/LIBRA in the full parameter space of WIMP effective models of inelastic scattering

We discuss the compatibility of the combined annual modulation effect measured by DAMA/LIBRA-phase1 and DAMA/LIBRA-phase2 with an explanation in terms of inelastic scattering events induced by the most general Galilean-invariant effective contact interaction of a Weakly Interacting Massive Particle (WIMP) dark matter particle of spin 0, 1/2 or 1. We take into account all the possible interferences among operators by studying the intersections among the ellipsoidal surfaces of constant signal of DAMA and other experiments in the space of the coupling constants of the effective theory. In our analysis we assume a standard Maxwellian velocity distribution in the Galaxy. We find that, compared to the elastic case, inelastic scattering partially relieves but does not eliminate the existing tension between the DAMA effect and the constraints from the null results of other experiments. Such tension is very large in all the parameter space with the exception of a small region for WIMP mass $m_χ\simeq$ 10 GeV and mass splitting $δ\gtrsim$ 20 keV, where it is partially, but not completely relieved. In such region the bounds from fluorine targets are evaded in a kinematic way because the minimal WIMP incoming speed required to trigger upscatters off fluorine exceeds the maximal WIMP velocity in the Galaxy, or is very close to it. As a consequence, we also find that the residual tension between DAMA and other results is more sensitive on the astrophysical parameters compared to the elastic case. We find that the configurations with the smallest tension can produce enough yearly modulation in some of the DAMA bins in compliance with the constraints from other experiments, but the ensuing shape of the modulation spectrum is too steep compared to the measured one. For such configurations the recent COSINE-100 bound is evaded in a natural way due to their large expected modulation fractions.

hep-ph↗

arXiv2019

Present and projected sensitivities of Dark Matter direct detection experiments to effective WIMP-nucleus couplings

Assuming for Weakly Interacting Massive Particles (WIMPs) a Maxwellian velocity distribution in the Galaxy we explore in a systematic way the relative sensitivity of an extensive set of existing and projected Dark Matter (DM) direct detection experiments to each of the 14 couplings that parameterize the most general non-relativistic (NR) effective Hamiltonian allowed by Galilean invariance for a contact interaction driving the elastic scattering off nuclei of WIMPs of spin 1/2. We perform our analysis in terms of two free parameters: the WIMP mass $m_χ$ and the ratio between the WIMP-neutron and the WIMP-proton couplings $c^n/c^p$. We include the modified signal spectral shape due to non-standard interactions when it is needed in the determination of the bound, such as in the case of background subtraction or of the application of the optimal-interval method. For each coupling, in the $m_χ$-$c^n/c^p$ plane we provide contour plots of the most stringent 90 % C.L. bound on the WIMP-nucleon cross section and show the experiment providing it. We also introduce NRDD_constraints, a simple interpolating code written in Python that allows to obtain the numerical value of the bound as a function of the WIMP mass $m_χ$ and of the coupling ratio $c^n/c^p$ for each NR coupling. We find that 9 experiments out of the 14 present Dark Matter searches considered in our analysis provide the most stringent bound on some of the effective couplings for a given choice of $(m_χ,c^n/c^p)$: this is evidence of the complementarity of different target nuclei and/or different combinations of count-rates and energy thresholds when the search of DM is extended to a wide range of possible interactions.

hep-ph↗