Threshold effects and renormalization group evolution of neutrino parameters in TeV scale seesaw models

We consider the threshold effect on the renormalization group (RG) evolution of the neutrino masses and mixing angles in TeV scale seesaw models. We obtain the analytic expressions using the factorization method in presence of threshold effects. We also perform numerical study of RG effects in two specific low scale seesaw models following the bottom-up approach and ascertain the role of seesaw thresholds in altering the values of masses and mixing angles during RG evolution.Comment: 31 pages, 8 figure

Vacuum Stability Constraints on the Minimal Singlet TeV Seesaw Model

We consider the minimal seesaw model in which two gauge singlet right handed neutrinos with opposite lepton numbers are added to the Standard Model. In this model, the smallness of the neutrino mass is explained by the tiny lepton number violating coupling between one of the singlets with the standard left-handed neutrinos. This allows one to have the right handed neutrino mass at the TeV scale as well as appreciable mixing between the light and heavy states. This model is fully reconstructible in terms of the neutrino oscillation parameters apart from the overall coupling strengths. We show that the overall coupling strength $y_\nu$ for the Dirac type coupling between the left handed neutrino and one of the singlets can be restricted by consideration of the (meta)stability bounds on the electroweak vacuum. In this scenario the lepton flavor violating decays of charged leptons can be appreciable which can put further constraint on $y_\nu$, for right-handed neutrinos at TeV scale. We discuss the combined constraints on $y_\nu$ for this scenario from the process $\mu \rightarrow e \gamma$ and from the consideration of vacuum (meta)stability constraints on the Higgs self coupling. We also briefly discuss the implications for neutrinoless double beta decay and possible signatures of the model that can be expected at colliders.Comment: One loop effective potential due to heavy neutrino included, 20 pages, 9 figure

N—H⋯N hydrogen bonding in 4,6-diphenyl-2-pyrimidinylamine isolated from the plant Justicia secunda (Acanthaceae)

The title compound, C₁₆H₁₃N₃, isolated from Justicia secunda (Acanthaceae), comprises two molecules (which differ slightly in conformation) in the asymmetric unit of space group P\overline 1. Intermolecular Namino-H...Npyrm interactions (Npyrm is a pyrimidine ring N atom) involve only one of the two donor amino H atoms and pyrimidine N atoms per molecule, forming dimeric units via R²₂(8) rings, with N...N distances of 3.058 (2) and 3.106 (3) Å, and N-H...N angles of 172.7 (18) and 175.8 (17)°. The dimers are linked by C-H...π(arene) contacts, with an H...centroid distance of 2.77 Å and a C-H...centroid angle of 141°

Naturalness, Vacuum Stability and Leptogenesis in the Minimal Seesaw Model

The right-handed neutrinos within the type-I seesaw mechanism can induce large radiative corrections to the Higgs mass, and naturalness arguments can then be used to set limits on their mass scale and Yukawa couplings. Driven by minimality, we consider the presence of two degenerate right-handed neutrinos. We compare the limits from naturalness with the ones from the stability of the electroweak vacuum and from lepton flavor violation. Implications from neutrinoless double beta decay are also discussed and renormalization effects for the light neutrino parameters are presented. Adding small perturbations to the degenerate heavy neutrino spectrum allows for successful leptogenesis.Comment: 22 pages, 11 figures; minor changes; version to appear in Phys. Rev.

A family of mixed ligand complexes of Ru<SUP>II</SUP>-L [L=N-aryl-pyridine-2-aldimine], their reactions, isolation and characterization. X-ray crystal structure of [Ru(pic)(L<SUP>1</SUP>)<SUB>2</SUB>][ClO<SUB>4</SUB>]. CH<SUB>2</SUB>Cl<SUB>2</SUB> [pic= 2-picolinate ion]

Synthesis of the tris-chelated complexes [Ru(L)n(L3)3-n]2+ (L=N-aryl-pyridine-2-aldimine, L3=2-(m-tolylazo)pyridine) based on silver(I) assisted trans-metallation is described. The complexes, [Ru(L)3]2+ and [Ru(L)(L3)2]2+ afford [Ru(pic)(L)2]+ and [Ru(pic)(L3)2]+ (pic= 2-picolinate ion) respectively, on hydrolysis and subsequent oxidation. When RuCl2(L)2 was reacted with two moles of [Ag(L3)2]+, a pink complex of composition [Ru(L)(L3)(L4)]+ [L4=N-aryl-2-picolinamide] was isolated along with the expected brown complex, [Ru(L3)(L)2]2+. Initial oxidation of the metal ion favours L&#8594;L4 conversion. The complexes have been characterized using spectroscopy and X-ray crystallography. The X-ray structure of [Ru(pic) (L1)2]ClO4.CH2Cl2 is reported. The metal oxidation as well as ligand reductions for the complexes have been studied voltammetrically in acetonitrile using platinum as the working electrode. It has been observed that the oxidation of the transformed complexes, viz. [Ru(pic) (L)2]+, [Ru(pic)(L3)2]+ and [Ru(L)(L3)(L4)]+ occur at lower potentials as compared to their parent [Ru(L)n(L3)3-n]2+ complexes. All the complexes show metal-to-ligand charge transfer transitions in the visible range and absorption energies linearly correlate with the differences between the metal oxidation and the first ligand reduction potentials