Dinesh Kumar

We investigate several phenomenological dark energy parameterizations using a joint analysis of late-time cosmological observations, including cosmic-chromatometer measurements of the Hubble parameter, DESI DR2 baryon acoustic oscillation data, and the Pantheon+ Type Ia supernova sample. Our results show that allowing for a time-varying dark energy equation of state significantly improves the overall fit compared to ΛCDM. The present-day equation-of-state parameter departs from the standard cosmological constant value. In contrast, the evolution parameter in two-parameter models tends to be negative, indicating a possible time dependence of dark energy. However, the constraints on the evolution remain moderate, and current data cannot clearly distinguish the specific functional form of dark energy. Model comparison using information criteria suggests that dynamical dark energy models are favored over ΛCDM, with the most straightforward one-parameter extension emerging as the most parsimonious scenario. These findings indicate a mild preference for dark energy evolution, though future high-precision observations will be required for definitive conclusions.

We investigate several phenomenological dark energy parameterizations using a joint analysis of late-time cosmological observations, including cosmic-chromatometer measurements of the Hubble parameter, DESI DR2 baryon acoustic oscillation data, and the Pantheon+ Type Ia supernova sample. Our results show that allowing for a time-varying dark energy equation of state significantly improves the overall fit compared to ΛCDM. The present-day equation-of-state parameter departs from the standard cosmological constant value. In contrast, the evolution parameter in two-parameter models tends to be negative, indicating a possible time dependence of dark energy. However, the constraints on the evolution remain moderate, and current data cannot clearly distinguish the specific functional form of dark energy. Model comparison using information criteria suggests that dynamical dark energy models are favored over ΛCDM, with the most straightforward one-parameter extension emerging as the most parsimonious scenario. These findings indicate a mild preference for dark energy evolution, though future high-precision observations will be required for definitive conclusions.

We present a comprehensive analysis of the decay Λ c − → Λ ( → p π ) μ − ν ¯ μ within a model-independent effective field theory framework. Previous studies have been restricted to the three-body decay Λ c + → Λ μ + ν μ and considered only left-handed neutrinos within the low-energy effective theory (LEFT). In this work, we extend the analysis to the complete four-body angular distribution for the first time, incorporating the indirect constraints implied by the Standard Model effective field theory (SMEFT) on the LEFT Wilson coefficients. We also include the effects of right-handed neutrino (RHN) operators, enabling a unified treatment of both left- and right-handed neutrino interactions in the c → s μ ν μ transition. Using the global bounds derived from LEFT observables and their SMEFT correlations, we study the impact of allowed new-physics scenarios on a variety of observables, including differential decay rates, forward-backward asymmetries, polarization asymmetries of the final-state hadron and lepton, and the angular coefficients ( M 0 to M 9 ) in the 4-body angular distribution. Our analysis reveals significant deviations from the Standard Model in the observables P L Λ and M 1 for C R L V and C R R V , and striking T -odd effects in M 7 for complex C R L V . These features provide sensitive probes of vector-type new physics, such as leptoquark or right-handed current models. The predicted patterns can be tested in forthcoming measurements at BESIII, LHCb, and Belle II, where polarization-sensitive observables in Λ c decays are becoming experimentally accessible.

We analyze the new physics (NP) effects in semileptonic B ¯ s → K * + ( → K π ) ℓ − ν ¯ ℓ decay induced by the b → uℓν _ℓ quark level transition. We consider the vector, scalar and tensor NP Lorentz structures in addition to the standard model in effective field theory approach. Constraints on NP parameters are obtained from experimental observations of both semileptonic and leptonic decays of B mesons, which are governed by the underlyng b → uℓν _ℓ transition. We explore the NP effects in differential branching fraction, lepton forward–backward asymmetry, fraction of longitudinal polarization of K * meson and normalized angular observables in B ¯ s → K * + ( → K π ) ℓ − ν ¯ ℓ decay.

We perform a model-independent study of c → sµν mediated transitions to analyze the new physics effects in the presence of right-handed neutrinos. We have adopted the effective field theory approach and write the lowenergy effective Hamiltonian including all possible dimension-six operators. The Wilson coefficients introduced through low energy effective Hamiltonian encode all New Physics that can enter in c → s transition at the dimension-six operator level. These Wilson coefficients are determined through a χ² fit by using the Miniut package to available experimental data of leptonic D_s⁺ → µ⁺ν_µ and semileptonic decays D⁰ → K⁻µ⁺ν_µ, D⁺ → K¯0µ⁺ν_µ and D⁰ → K^∗−µ⁺ν_µ, D⁺ → K¯∗0µ⁺ν_µ, D_s⁺ → φµ⁺ν_µ. The differential decay width of B_c⁺ → B_sµ⁺ν_µ is derived to investigate the role of right-handed neutrinos in the search for new physics through the three-body decay process. We also make the predictions of q² spectra for the mode B_c⁺ → B_sμ⁺ν_μ to inspect the effect of the allowed new physics in c → s sector through right-handed neutrinos to motivate the future measurements.