N Nimai Singh
Articles written in Pramana – Journal of Physics
Volume 60 Issue 2 February 2003 pp 405-409
Working group report: Neutrino and astroparticle physics
Raj Gandhi Kamales Kar S Uma Sankar Abhijit Bandyopadhyay Rahul Basu Pijushpani Bhattacharjee Biswajoy Brahmachari Debrupa Chakraborti M Chaudhury J Chaudhury Sandhya Choubey E J Chun Atri Desmukhya Anindya Datta Gautam Dutta Sukanta Dutta Anjan Giri Sourendu Gupta Srubabati Goswami Namit Mahajan H S Mani A Mukherjee Biswarup Mukhopadhyaya S N Nayak M Randhawa Subhendu Rakshit Asim K Ray Amitava Raychaudhuri D P Roy Probir Roy Suryadeep Roy Shiv Sethi G Sigl Arunansu Sil N Nimai Singh Mark Vagins Urjit Yagnik
This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.
Volume 65 Issue 6 December 2005 pp 1015-1025
New uncertainties in QCD—QED rescaling factors using quadrature method
In this paper we briefly outline the quadrature method for estimating uncertainties in a function which depends on several variables, and apply it to estimate the numerical uncertainties in QCD-QED rescaling factors. We employ here the one-loop order in QED and three-loop order in QCD evolution equations of the fermion mass renormalisation. Our present calculation is found to be new and also reliable when compared to the earlier values employed by various authors
Volume 66 Issue 2 February 2006 pp 361-375
Discriminating neutrino mass models using type-II see-saw formula
N Nimai Singh Mahadev Patgiri Mrinal Kumar Das
An attempt has been made to discriminate theoretically the three possible patterns of neutrino mass models,viz., degenerate, inverted hierarchical and normal hierachical models, within the framework of Type-II see-saw formula. From detailed numerical analysis we are able to arrive at a conclusion that the inverted hierarchical model with the same CP phase (referred to as Type [IIA]), appears to be most favourable to survive in nature (and hence most stable), with the normal hierarchical model (Type [III]) and inverted hierarchical model with opposite CP phase (Type [IIB]), follow next. The degenerate models (Types [IA,IB,IC]) are found to be most unstable. The neutrino mass matrices which are obtained using the usual canonical see-saw formula (Type I), and which also give almost good predictions of neutrino masses and mixings consistent with the latest neutrino oscillation data, are re-examined in the presence of the left-handed Higgs triplet within the framework of non-canonical see-saw formula (Type II). We then estimate a parameter (the so-called discriminator) which may represent the minimum degree of suppression of the extra term arising from the presence of left-handed Higgs triplet, so as to restore the good predictions on neutrino masses and mixings already acquired in Type-I see-saw model. The neutrino mass model is said to be favourable and hence stable when its canonical see-saw term dominates over the non-canonical (perturbative) term, and this condition is used here as a criterion for discriminating neutrino mass models.
Volume 69 Issue 4 October 2007 pp 533-549 Research Articles
N Nimai Singh Monisa Rajkhowa Abhijit Borah
We explore a novel possibility for lowering the solar mixing angle ($\theta_{12}$) from tri-bimaximal mixings, without sacriﬁcing the predictions of maximal atmospheric mixing angle ($\theta_{23} = 45^{\circ}$) and zero reactor angle ($\theta_{13} = 0^{\circ}$) in the inverted and normal hierarchical neutrino mass models having 2-3 symmetry. This can be done through the identiﬁcation of a ﬂavour twister term in the texture of neutrino mass matrix and the variation of such term leads to lowering of solar mixing angle. For the observed ranges of $\Delta m_{21}^{2}$ and $\Delta m_{23}^{2}$, we calculate the predictions on tan^{2} $\theta_{12} = 0.5, 0.45, 0.35$ for different input values of the parameters in the neutrino mass matrix. We also observe a possible transition from inverted hierarchical model having even CP parity (Type-IHA) to inverted hierarchical model having odd CP parity (Type-IHB) in the ﬁrst two mass eigenvalues, when there is a change in input values of parameters in the same mass matrix. The present work differs from the conventional approaches for the deviations from tri-bimaximal mixing, where the 2-3 symmetry is broken, leading to $\theta_{23} \neq 45^{\circ}$ and $\theta_{13} \neq 0^{\circ}$.
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