arXiv subjects

Biswajit Das

Publications and source records attributed to Biswajit Das.

At least 37 records · Page 2Linked to original sources

arXiv2024

Probing Anomalous Higgs Boson Couplings at Colliders

In this thesis, our main focus is on the $HHH$ and $VVHH$ couplings which are loosely bound. The $HHH$ coupling will determine the shape the Higgs potential and $VVHH$ couplings will tell us how the gauge bosons are coupled to the Higgs fields. We consider a few processes of Higgs boson production and decay to study these couplings. We calculate one-loop QCD and electroweak correction for these processes. In this thesis, we discuss spinor helicity formalism, which has been used in computing Feynman amplitudes for QCD and electroweak correction to these processes. We discuss one-loop Feynman integrals and one-loop electroweak renormalization and Catani-Seymour dipole subtraction scheme in this thesis. We compute all possible self-energy contributions at one-loop for electroweak renormalization. In this thesis, in the first work, we consider the process $b\bar{b}\rightarrow W^+W^-H$. Due to the non-negligible coupling of the Higgs boson with the bottom quarks, there is a dependence on the $WWHH$ coupling in this process. We find that the corrections to the final state with the longitudinally polarized $W$ bosons are large. In the second work, we study one-loop electroweak correction to $H\rightarrow ν_e\bar{ν_e}ν_μ\bar{ν_μ}$. We discuss $γ^5$-anomaly, complex mass scheme and input parameter schemes which are relevant for one-loop electroweak correction. The corrections depend on the $HHH$ and $ZZHH$ couplings. We investigate this dependence in $κ$-framework. In the third work, we study one-loop electroweak correction to the $H\rightarrow e^+e^-μ^+μ^-$ process. The corrections depend on $HHH$ and $ZZHH$ couplings. We observe the same behavior in the relative change of the decay width for this process as the process $H\rightarrow ν_e\bar{ν_e}ν_μ\bar{ν_μ}$ when we vary $HHH$ and $ZZHH$ couplings.

hep-ph↗

arXiv2024

Effect of anomalous $HHH$ and $ZZHH$ couplings on the decay width of $H\rightarrow ν_e\barν_eν_μ\barν_μ$

Despite the discovery of the Higgs boson, the Higgs sector of the standard model is still not fully established. In particular, the self couplings of the Higgs boson, and its couplings with gauge bosons, are still to be fully determined. We consider electroweak corrections to the process $H\rightarrow ν_e\barν_eν_μ\barν_μ$. The corrections depend on the $HHH$ and $ZZHH$ couplings. We investigate this dependence in $κ$-framework. We find that the width depends on $HHH$ coupling significantly. The dependence on $ZZHH$ coupling is only marginal. We also discuss the dependence on $ZZWW$ coupling.

hep-ph↗

arXiv2024

Barrier height inhomogeneity and origin of 1/f-noise in topological insulator-based photo-detector

Topological insulators (TIs) with symmetry-protected surface states, offer exciting opportunities for next-generation photonic and optoelectronic device applications. The heterojunctions of TIs and semiconductors (e.g. Si, Ge) have been observed to excellent photo-responsive characteristics. However, the realization of high-frequency operations in these heterojunctions can be hindered by unwanted 1/f (or Flicker) noise and phase noise. Therefore, an in-depth understanding of 1/f noise figures becomes paramount for the effective utilization of such materials.Here we report optoelectronic response and 1/f noise characteristics of a p-n diode fabricated using topological insulator, Bi2Se3 and silicon for potential photo-detector. Through meticulous temperature-dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements, we ascertain crucial parameters like barrier height, ideality factor, and reverse saturation current of the photodetector. The low-frequency 1/f conductance noise spectra suggest a significant presence of trap states influencing the optoelectronic transport properties. The forward noise characteristics exhibit typical 1/f features, having a uni-slope across four decades of frequency, suggesting a homogeneous distribution of barrier height. The spectral and photocurrent-dependent responses show the power law behavior of noise level on photon flux. The hybrid heterojunction demonstrates excellent photo-response and reasonably low noise level, promising signatures for the room-temperature visible photodetector applications.

cond-mat.str-el↗

arXiv2024

In-beam $γ-$spectroscopy of the transitional nucleus $^{217}$Ac

High-spin states in the transitional $^{217}$Ac nucleus are established up to 3.8 MeV excitation energy and $I^π =$ 41/2$^+$ with the addition of around 20 new transitions. The structure of the yrast and near-yrast states below the 29/2$^+$ isomer is revisited. The inconsistencies in the level schemes reported earlier are resolved. The level structure above the 29/2$^+$ isomer is established for the first time. Large-basis shell-model calculations with the KHPE interaction are performed to compare the experimentally observed level energies with the theoretical predictions. A comparison with the systematics of the N = 128 isotones suggests that the yrast structures result from a weak coupling of the odd proton to the even-even 216Ra core, which is consistent with the shell-model configurations. Furthermore, alpha decay of the 29/2$^+$ isomer is revisited and the decay scheme established from this work is discussed in the framework of the shell model.

nucl-ex↗

arXiv2024

Square-free Word-representation of Word-representable Graphs

A graph $G = (V, E)$ is word-representable, if there exists a word w over the alphabet V such that for letters ${x, y} \in V$ , $x$ and $y$ alternate in $w$ if and only if $xy \in E$. In this paper, we prove that any non-empty word-representable graph can be represented by a word containing no non-trivial squares. This result provides a positive answer to the open problem present in the book Words and graphs written by Sergey Kitaev, and Vadim Lozin. Also, we prove that for a word-representable graph $G$, if the representation number of $G$ is $k$, then every $k$-uniform word representing the graph $G$ is also square-free. Moreover, we prove that every minimal-length word representing a graph is square-free. Then, we count the number of possible square-free word-representations of a complete graph. At last, using the infinite square-free string generated from the Thue-Morse sequence, we prove that infinitely many square-free words represent a non-complete connected word-representable graph.

math.CO↗

arXiv2023

Enhanced directionality of active processes in a viscoelastic bath

Active fluctuations are known to play a significant role in the intracellular transport of passive objects. However, the effect of viscoelasticity of the environment in shaping such processes is relatively less understood. Here, with a minimal experiment using a driven colloid in a viscoelastic bath, we show that viscoelasticity significantly increases the mean injected power to the passive object ($\sim 50\%$ compared to a viscous medium), for the same strength of the external driving. Additionally, we observe a notable reduction in negative work fluctuations across a wide range of driving amplitudes. These findings collectively suggest an enhanced directionality in driven processes within a viscoelastic bath, which we attribute to the emergence of interactions between the colloid and the viscoelastic medium.

cond-mat.stat-mech↗

arXiv2023

A study of holographic dark energy models using configuration entropy

The holographic dark energy models provide an alternative description of the dark energy. These models are motivated by the possible application of holographic principle to the dark energy problem. We study the one parameter Li holographic dark energy and the two parameter Barrow holographic dark energy models using configuration entropy of the matter distribution in the Universe. The configuration entropy rate exhibits a distinct minimum at a specific scale factor that corresponds to the epoch, beyond which the dark energy takes a driving role in the accelerated expansion of the Universe. We find that the location of the minimum and magnitude of the entropy rate at the minimum are sensitive to the parameters of the models. We find the best fit relations between these quantities and the parameters of each model. We propose that these relations can be used to constrain the parameters of the holographic dark energy models from the future measurements of the configuration entropy at multiple redshifts. Further, the Barrow holographic dark energy model is based on Barrow entropy which modifies the standard Bekenstein-Hawking entropy, to capture the deformation of the black-hole surface due to quantum gravitational effects. We find that the location and amplitude of the minimum of the configuration entropy rate is strongly sensitive to the deformation exponent $Δ$ in the Barrow model. Our study suggests that signatures of the quantum gravitational effects on the future event horizon may be detected from the study of the configuration entropy of the matter distribution on large-scales.

astro-ph.CO↗

arXiv2022

Inferring entropy production in anharmonic Brownian gyrators

A non-vanishing entropy production rate is one of the defining characteristics of any non-equilibrium system, and several techniques exist to determine this quantity directly from experimental data. The short-time inference scheme, derived from the thermodynamic uncertainty relation, is a recent addition to the list of these techniques. Here we apply this scheme to quantify the entropy production rate in a class of microscopic heat engine models called Brownian gyrators. In particular, we consider models with anharmonic confining potentials. In these cases, the dynamical equations are indelibly non-linear, and the exact dependences of the entropy production rate on the model parameters are unknown. Our results demonstrate that the short-time inference scheme can efficiently determine these dependencies from a moderate amount of trajectory data. Furthermore, the results show that the non-equilibrium properties of the gyrator model with anharmonic confining potentials are considerably different from its harmonic counterpart - especially in set-ups leading to a non-equilibrium dynamics and the resulting gyration patterns.

cond-mat.stat-mech↗

arXiv2022

Non-monotonic skewness of currents in non-equilibrium steady states

Measurements of any property of a microscopic system are bound to show significant deviations from the average, due to thermal fluctuations. For time-integrated currents such as heat, work or entropy production in a steady state, it is in fact known that there will be long stretches of fluctuations both above as well as below the average, occurring equally likely at large times. In this paper we show that for any finite-time measurement in a non-equilibrium steady state - rather counter-intuitively - fluctuations below the average are more probable. This discrepancy is higher when the system is further away from equilibrium. For overdamped diffusive processes, there is even an optimal time when time-integrated current fluctuations mostly lie below the average. We demonstrate that these effects result from the non-monotonic skewness of current fluctuations and provide evidence that they are easily observable in experiments. We also discuss their extensions to discrete space Markov jump processes and implications to biological and synthetic microscopic engines.

cond-mat.stat-mech↗

arXiv2022

Revisiting the magnetic ordering through anisotropic magnetic entropy change in quasi-two-dimensional metallic ferromagnet, Fe$_4$GeTe$_2$

We have investigated the nature of ferromagnetic order and phase transitions in two dimensional (2D) van der Waals (vdW) layered material, Fe$_4$GeTe$_2$ through measurements of magnetization, magneto-caloric Effect (MCE), and heat capacity. Fe$_4$GeTe$_2$ hosts a complex magnetic phase with two distinct transitions: paramagnetic to ferromagnetic at around $T_\text{C}$ $\sim$ 266 K and another spin reorientation transition (SRT) at around $T_\text{SRT}$ $\sim $ 100 K. The magnetization measurements shows a prominent thermal hysteresis in proximity to $T_\text{SRT}$ at $H\parallel c$, which implies the first-order nature of SRT. Reasonable MCE has been observed around both transition temperatures ( at around $T_\text{C}$, -$Δ$S$_M^\text{max}$ = 1.95 and 1.99 J.Kg$^{-1}$K$^{-1}$ and at around $T_\text{SRT}$, -$Δ$S$_M^\text{max}$= 3.9 and 2.4 J.Kg$^{-1}$K$^{-1}$ along $H\parallel ab$ and $H\parallel c$ respectively) at 50 kOe magnetic field change. The above results reveal higher MCE value at $T_\text{SRT}$ compared to the values of MCE at $T_\text{C}$. The scaling analysis of MCE at $T_\text{C}$, shows that the rescaled $Δ$S$_M (T, H)$ follow a universal curve confirming the second-order character of the ferromagnetic transition. The same scaling analysis of MCE breaks down at $T_\text{SRT}$ suggesting that SRT is not a second order phase transition. The exponent $n$ from field dependence of magnetic entropy change presents a maximum of $|n|>2$ confirming the first-order nature of SRT.

cond-mat.str-el↗

arXiv2022

Nonlinear coherent light-matter interaction in 2D MoSe$_2$ nanoflakes for all-optical switching and logic applications

We report a strong nonlinear optical response of 2D MoSe$_2$ nanoflakes (NFs) through spatial self-phase modulation (SSPM) and cross-phase modulation (XPM) induced by nonlocal coherent light-matter interactions. The coherent interaction of light and MoSe$_2$ NFs creates the SSPM of laser beams, forming concentric diffraction rings. The nonlinear refractive index ($n_2$) and the third-order broadband nonlinear optical susceptibility ($χ^{(3)}$) of MoSe$_2$ NFs are determined from the self diffraction pattern at different exciting wavelengths of 405, 532, and 671 nm with varying the laser intensity. The evolution and deformation of diffraction ring patterns are observed and analyzed by the `wind-chime' model and thermal effect. By taking advantage of the reverse saturated absorption of 2D SnS$_2$ NFs compared to MoSe$_2$, an all-optical diode has been designed with MoSe$_2$/SnS$_2$ hybrid structure to demonstrate the nonreciprocal light propagation. Also a few other optical devices based on MoSe$_2$ and other semiconducting materials such as Bi$_2$Se$_3$, CuPc, and graphene have been investigated. The all-optical logic gates and all-optical information conversion have been demonstrated through the XPM technique using two laser beams. The proposed optical scheme based on MoSe$_2$ NFs has been demonstrated as a potential candidate for all-optical nonlinear photonic devices such as all-optical diodes and all-optical switches.

physics.optics↗

arXiv2022

Experimental verification of Arcsine laws in mesoscopic non-equilibrium and active systems

A large number of processes in the mesoscopic world occur out of equilibrium, where the time course of a system evolution becomes immensely important since it is driven principally by dissipative effects. Non-equilibrium steady states (NESS) represent a crucial category in such systems, where relaxation timescales are comparable to the operational timescales. In this study, we employ a model NESS stochastic system which comprises of a colloidal microparticle, optically trapped in a viscous fluid, externally driven by a temporally correlated noise, and show that time-integrated observables such as the entropic current, the work done on the system or the work dissipated by it, follow the three Levy arcsine laws [1], in the large time limit. We discover that cumulative distributions converge faster to arcsine distributions when it is near equilibrium and the rate of entropy production is small, because in that case the entropic current has weaker temporal autocorrelation. We study this phenomenon changing the strength of the added noise or by perturbing our system with a flow field produced by a microbubble at close proximity to the trapped particle. We confirm our experimental findings with theoretical simulations of the systems. Our work provides an interesting insight into the NESS statistics of the meso-regime, where stochastic fluctuations play a pivotal role.

cond-mat.soft↗

arXiv2021

Superconductivity coexisting with ferromagnetism in a quasi-one dimensional non-centrosymmetric (TaSe$_4$)$_3$I

Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric (TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a non-magnetic insulator. The coexistence here upfront contradicts the popular belief that superconductivity and ferromagnetism are two apparently antagonistic phenomena. Notably, here, for the first time, we have clearly detected Meissner effect in the superconducting state despite the coexisting ferromagnetic order. The coexistence of superconductivity and ferromagnetism projects non-centrosymmetric (TaSe$_4$)$_3$I as a host for complex ground states of quantum matter including possible unconventional superconductivity with elusive spin-triplet pairing.

cond-mat.supr-con↗

arXiv2021

Quantitative analysis of non-equilibrium systems from short-time experimental data

We provide a minimal strategy for the quantitative analysis of a large class of non-equilibrium systems in a {statistically} steady state using the short-time Thermodynamic Uncertainty Relation (TUR). From short-time trajectory data obtained from experiments, we demonstrate how we can simultaneously infer quantitatively, both the thermodynamic force field acting on the system, as well as the (potentially exact) rate of entropy production. We benchmark this scheme first for an experimental study of a colloidal particle system where exact analytical results are known, before applying it to the case of a colloidal particle in a hydrodynamical flow field, where neither analytical nor numerical results are available. In this latter case, we build an effective model of the system based on our results. In both cases, we also demonstrate that our results match with those obtained from another recently introduced scheme [Phys. Rev. X 10, 021009].

cond-mat.soft↗

arXiv2021

A mechanistic model for the asymmetric torque-speed relationships of a bacterial flagellar motor

A tiny bacterial flagellar motor rotates in both counter-clockwise (CCW) and clockwise (CW) rotational directions. The most important measurable characteristic of the flagellar motor is its torque versus angular speed relationship in CCW or CW modes, which is found to be non-symmetrical with each other, and still, such a phenomenon is not clearly understood.Here, we explain this asymmetry through a mechanistic model based on the detailed torque analysis for the rotation of the motor and the revolutionary as well as spinning motion of the filament and bead. We find out that the asymmetry results from the conformational changing of the hook due to rotational switching, rather than any non-symmetric changes in the potential of mean force generated by the stator-rotor interactions. In CCW mode, when the hook remains bend and flexible, the revolution motion predominates and the restoring torque in this motion, originated due to drag, governs the shape of the torque-speed curve. However, in CW mode, spinning motion dominates as the hook becomes straight and rigid, and the linear torque-speed relation arises due to the restoring torque for the drag corresponding to this motion. Our study indicates the significant role of the hook's conformational change upon the biological functions of the motor and paves the way for further experimental exploration on the structural origin of such asymmetry.

physics.bio-ph↗

arXiv2021

$W^+W^-H$ production through bottom quarks fusion at hadron colliders

With the standard model working well in describing the collider data, the focus is now on determining the standard model parameters as well as for any hint of deviation. In particular, the determination of the couplings of the Higgs boson with itself and with other particles of the model is important to better understand the electroweak symmetry breaking sector of the model. In this letter, we look at the process $pp \to WWH$, in particular through the fusion of bottom quarks. Due to the non-negligible coupling of the Higgs boson with the bottom quarks, there is a dependence on the $WWHH$ coupling in this process. This sub-process receives largest contribution when the $W$ bosons are longitudinally polarized. We compute one-loop QCD corrections to various final states with polarized $W$ bosons. We find that the corrections to the final state with the longitudinally polarized $W$ bosons are large. It is shown that the measurement of the polarization of the $W$ bosons can be used as a tool to probe the $WWHH$ coupling in this process. We also examine the effect of varying $WWHH$ coupling in the $κ$-framework.

hep-ph↗

arXiv2020

Can we constrain the evolution of HI bias using configuration entropy?

We study the evolution of the configuration entropy of HI distribution in the post-reionization era assuming different time evolution of HI bias. We describe time evolution of linear bias of HI distribution using a simple form $b(a)=b_{0} a^{n}$ with different index $n$. The derivative of the configuration entropy rate is known to exhibit a peak at the scale factor corresponding to the $Λ$-matter equality in the unbiased $Λ$CDM model. We show that in the $Λ$CDM model with time-dependent linear bias, the peak shifts to smaller scale factors for negative values of $n$. This is related to the fact that the growth of structures in the HI density field can significantly slow down even before the onset of $Λ$ domination in presence of a strong time evolution of the HI bias. We find that the shift is linearly related to the index $n$. We obtain the best fit relation between these two parameters and propose that identifying the location of this peak from observations would allow us to constrain the time evolution of HI bias within the framework of the $Λ$CDM model.

astro-ph.CO↗

arXiv2019

Can we constrain the dark energy equation of state parameters using configuration entropy?

We propose a new scheme for constraining the dark energy equation of state parameter/parameters based on the study of the evolution of the configuration entropy. We analyze a set of one parameter and two parameter dynamical dark energy models and find that the derivative of the configuration entropy in all the dynamical dark energy models exhibit a minimum. The magnitude of the minimum of the entropy rate is decided by both the parametrization of the equation of state as well as the associated parameters. The location of the minimum of the entropy rate is less sensitive to the form of the parametrization but depends on the associated parameters. We determine the best fit equations for the location and magnitude of the minimum of the entropy rate in terms of the parameter/parameters of the dark energy equation of state. These relations would allow us to constrain the dark energy equation of state parameter/parameters for any given parametrization provided the evolution of the configuration entropy in the Universe is known from observations.

astro-ph.CO↗