arXiv subjects

Ajay Kumar Yadav

Publications and source records attributed to Ajay Kumar Yadav.

7 recordsLinked to original sources

arXiv2026

Quantifying the effect of passband on observations in the Ca II K line

Full-disk observations of the Sun in the Ca II K line have been carried out since the late 19th century at various observatories worldwide. These long-term records of solar activity are crucial for reducing discrepancies among solar irradiance reconstructions and for advancing our understanding of the solar dynamo. To construct a consistent composite record, data from different observatories must be cross-calibrated to account for variations in spectral passband and spatial resolution, which are the primary sources of discrepancies between archives. In this study, we use high spectral and spatial resolution observations in the Ca II K line from the state-of-the-art Sunrise III mission to emulate different passbands and derive empirical contrast-contrast relationships between them. We find that these relationships are well described by a power law and provide coefficients for different combinations of passband widths in the range 0.1--9 Angstroms and spatial resolutions between 1 arcsec and 6 arcsec. Applying such a relationship to observations from two major Ca II K archives demonstrates its potential to improve their cross-calibration. The results provide a foundation for the construction of a consistent, century-long time series of solar activity from historical and modern Ca II K observations.

astro-ph.SR↗

arXiv2024

Binwise exploration of vector couplings in $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ decays

Recent results from the LHCb experiment have confirmed that lepton flavor universality is upheld in flavor-changing neutral current processes, such as $B \to K^{(*)} l^+ l^-$. However, discrepancies remain in the charged current sector, raising questions about the universality of lepton flavors in these processes. To explore this issue, we investigate the decays $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ in different $q^2$ bins, which involve the $b \to c \tau \bar \nu_\tau$ transition. We employ a model-independent approach to analyze potential new physics by fitting both real and complex (axial)vector coefficients to the existing $b \to (u, c) \tau \bar \nu_\tau$ data. Our analysis enables us to calculate the branching ratios and angular distributions for the $B_s \to D_s^{(*)} \tau \bar \nu_\tau$ decays in four different $q^2$ bins. Additionally, we evaluate whether lepton flavor universality is maintained in these charged current decays or if deviations suggest the presence of new physics.

hep-ph↗

arXiv2024

Revealing the $q^2$ dependence in $b \to s \mu^+ \mu^-$ baryonic decay modes

Measurements from the LHCb experiment and $B$ factories have revealed several discrepancies in angular observables of rare semileptonic $B$ decays involving the quark-level transition $b \to s \ell^+ \ell^-$. In this work, we conduct a model-independent comparative analysis of the rare semileptonic decays of baryons $\Lambda_b$, $\Sigma_b$ and $\Xi_b$, exploring various new physics scenarios. Our analysis includes predictions for branching ratios and angular observables, including forward-backward asymmetry, longitudinal polarization fractions, and lepton flavor universality ratios, both within the Standard Model and across six distinct new physics scenarios. Notably, we find that certain new physics scenarios significantly affect the observables in the $(\Lambda_b, \Sigma_b, \Xi_b) \to (\Lambda, \Sigma, \Xi) \mu^+ \mu^-$ processes.

hep-ph↗

arXiv2024

Signature of (axial)vector operators in $B_c\to D_s^{(*)} \mu^+ \mu^-$ decays

The persistent anomalies observed in $B$ mesons related to $b \to s \mu^+ \mu^-$ transitions point to the potential for new physics beyond the Standard Model. To explore this further, we conduct an analysis of the exclusive semileptonic decays $B_c\to D_s^{(*)} \mu^+ \mu^-$ within an effective field theory formalism. We perform a global fit to new (axial)vector couplings using the current experimental data for $b \to s \mu^+ \mu^-$ transitions. We compute the branching ratios and physical observables such as forward-backward asymmetries, lepton polarization asymmetries, form factor independent observables for $B_c\to D_s^{(*)} \mu^+ \mu^-$, both within the Standard Model and in new physics scenarios. Additionally, we examine the existence of lepton flavor universality violation in the $B_c\to D_s^{(*)} \ell^+ \ell^-$ process.

hep-ph↗

arXiv2024

Analysis of the semileptonic $B_c\to D_s^*μ^+ μ^-$ decay mode in the effective field theory approach

Discrepancies have been noted between experimental measurements and Standard Model predictions for various observables related to the $B\to(K, K^*,ϕ) ll$ processes. Recently, the Belle-II Collaboration observed a $2.8σ$ deviation from Standard Model predictions in the branching ratio of the $B \to K ν_l \bar{ν_l}$ decay mode. In this context, we investigate the exclusive semileptonic $B_c\to D_s^{*}μ^+ μ^-$ decay mode, mediated by $b\to s$ quark level transition, using Effective Field Theory formalism. We perform a global fit to the new parameters using existing experimental data on $b \to s μ^+ μ^-$. We then estimate the branching ratio and other observables such as forward-backward asymmetry, lepton polarisation asymmetry, and the lepton non-universality parameter of the $B_c\to D_s^{(*)}μ^+ μ^-$ process. Although this process has not yet been detected experimentally, we offer predictions and discuss the observables for $B_c\to D_s^{*}μ^+ μ^-$ in both the Standard Model and potential new physics scenarios.

hep-ph↗

arXiv2024

GeV scale dark matter and $B\rightarrow K+$ missing energy phenomenology in the $U(1)_{B-L}$ model

We elucidate the recently observed discrepancy in the branching ratio of $B^{+}\rightarrow K^{+}$ +inv decay mode using a GeV scale scalar dark matter in an anomaly-free $U(1)_{B-L}$ gauge extension of the Standard Model. We constrain the new parameters by using consistency with the existing bounds on Dark matter relic density, direct detection, collider and BR($B\rightarrow K^*ν\barν$) measured at the Belle II experiment. We investigate couplings between the mediator and the SM fermions as well as the dark matter particle. We then estimate the branching ratios of $b \to s ν\bar ν$ decay processes such as $B\rightarrow (K^+,K^*)ν\barν$, $B_s\rightarrow (η,η')ν\barν$, $ B_s\rightarrow ϕν\barν$ and $B_c\rightarrow (D_s, D_s^*)ν\barν$ in a common parameter space, meeting the current experimental bounds of both sectors simultaneously.

hep-ph↗

arXiv2022

Relatively normal-slant helices in Minkowski $3$-space

In this paper, we study relatively normal-slant helices lying on timelike as well as spacelike surfaces in Minkowski $3$-space $ \mathbb{E}_1^3$. The axes of spacelike and timelike relatively normal-slant helices are obtained via their Darboux frames. We also establish characterization theorems for spacelike and timelike relatively normal-slant helices in Minkowski $3$-space $\mathbb{E}_1^3$. Finally, the relationship between relatively normal-slant helices and slant helices is found on timelike as well as spacelike surfaces.

math.GM↗