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Agarwalla, S. K., Prakash, S., Raut, S. K., & Sankar, S. U. (2012). Potential of optimized NOvA for large theta(13) and combined performance with a LArTPC & T2K. J. High Energy Phys., 12(12), 075–21pp.
Abstract: NO nu A experiment has reoptimized its event selection criteria in light of the recently measured moderately large value of theta(13). We study the improvement in the sensitivity to the neutrino mass hierarchy and to leptonic CP violation due to these new features. For favourable values of delta(CP), NO nu A sensitivity to mass hierarchy and leptonic CP violation is increased by 20%. Addition of 5 years of neutrino data from T2K to NO nu A more than doubles the range of delta(CP) for which the leptonic CP violation can be discovered,compared to stand alone NO nu A. But for unfavourable values of delta(CP), the combination of NO nu A and T2K are not enough to provide even a 90% C.L. hint of hierarchy discovery. Therefore,we further explore the improvement in the hierarchy and CP violation sensitivities due to the addition of a 10 kt liquid argon detector placed close to NO nu A site. The capabilities of such a detector are equivalent to those of NO nu A in all respects. We find that combined data from 10 kt liquid argon detector (3 years of nu + 3 years of (nu) over bar run), NO nu A (6 years of nu + 6 years of nu run) and T2K (5 years of nu run) can give a close to 2 sigma hint of hierarchy discovery for all values of delta(CP). With this combined data,we can achieve CP violation discovery at 95% C.L. for roughly 60% values of delta(CP).
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Agarwalla, S. K., Prakash, S., & Sankar, S. U. (2013). Resolving the octant of theta(23) with T2K and NOvA. J. High Energy Phys., 07(7), 131–24pp.
Abstract: Preliminary results of MINOS experiment indicate that theta(23) is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for theta(23): one in the lower octant (LO: theta(23) < 45 degrees) and the other in the higher octant (HO: theta(23) > 45 degrees). v(mu) -> v(e) oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOvA experiments. Because of the hierarchy-delta(CP) degeneracy and the octant delta(CP) degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of delta(CP) for which octant resolution is easy (challenging). However, for octant resolution the unfavorable delta(CP) values of the neutrino data are favorable for the anti-neutrino data and vice-verse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NOvA to resolve the octant ambiguity. If sin(2)theta(23) – 0.41, then NOvA can rule out all the values of theta(23) in HO at 2 sigma C.L., irrespective of the hierarchy and delta(CP). Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and anti-neutrino runs of 2.5 years each, a 2 sigma resolution of the octant becomes possible provided sin(2) theta(23) <= 0.43 or >= 0.58 for any value of delta(CP).
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Banerjee, U., Chakraborty, S., Prakash, S., & Rahaman, S. U. (2024). Feasibility of ultrarelativistic bubbles in SMEFT. Phys. Rev. D, 110(5), 055002–17pp.
Abstract: A first order electroweak phase transition probes physics beyond the Standard Model on multiple frontiers and therefore is of immense interest for theoretical exploration. We conduct a model-independent study of the effects of relevant dimension 6 and dimension 8 operators, of the Standard Model effective field theory, on electroweak phase transition. We use a thermally corrected and renormalization group improved potential and study its impact on nucleation temperature. We then outline bubble dynamics that lead to ultrarelativistic bubble wall velocities which are mainly motivated from the viewpoint of gravitational wave detection. We highlight the ranges of the Wilson coefficients that give rise to such bubble wall velocities and predict gravitational wave spectra generated by such transitions which can be tested in future experiments.
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Chowdhury, D., Hait, A., Mohanty, S., & Prakash, S. (2024). Ultralight dark matter explanation of NANOGrav observations. Phys. Rev. D, 110(8), 083023–10pp.
Abstract: The angular correlation of pulsar residuals observed by NANOGrav and other pulsar timing array collaborations show evidence in support of the Hellings-Downs correlation expected from stochastic gravitational wave background (SGWB). In this paper, we offer a nongravitational wave explanation of the observed pulsar timing correlations as caused by an ultralight L μ- L z gauge boson dark matter (ULDM). ULDM can affect the pulsar correlations in two ways. The gravitational potential of vector ULDM gives rise to a Shapiro time delay of the pulsar signals and a nontrivial angular correlation (as compared to the scalar ULDM case). In addition, if the pulsars have a nonzero charge of the dark matter gauge group, then the electric field of the local dark matter causes an oscillation of the pulsar and a corresponding Doppler shift of the pulsar signal. We point out that pulsars carry a significant charge of muons, and thus the L μ- L z vector dark matter contributes to both the Doppler oscillations and the time delay of the pulsar signals. The synergy between these two effects provides a better fit to the shape of the angular correlation function, as observed by the NANOGrav collaboration, compared to the standard SGWB explanation or the SGWB combined with time delay explanations. Our analysis shows that, in addition to the SGWB signal, there may potentially be excess timing residuals attributable to the L μ- L z ULDM.
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