arXiv subjects

Arun M. Thalapillil

Publications and source records attributed to Arun M. Thalapillil.

21 records · Page 2Linked to original sources

arXiv2010

Bound states and fermiophobic Unparticle oblique corrections to the photon

We study the effects of fermiophobic scalar/pseudo-scalar oblique corrections on bound state energy levels in muonic atoms. To make the treatment sufficiently general we will consider Unparticle scalars/pseudo-scalars which couple only to photons. We derive the relevant vacuum polarization functions and comment on the functional forms of the Unparticle Uehling potentials for various scaling dimensions in the point nucleus and finite nucleus approximations. It is estimated that for an infra-red fixed point near the scale of electroweak symmetry breaking, in the low TeV range, the energy shifts in the low-lying muonic lead transitions could typically be of the order of a few times 0.1 eV to a few times 0.01 eV. It is shown that this conclusion is not changed even when scale invariance is broken and is in fact relatively insensitive to the scale at which it is broken. It is pointed out nevertheless that the estimated magnitude of the Unparticle Uehling shift is a factor of $10^{3}-10^{4}$ below the discrepancy in QED/nuclear theory and precision muonic lead spectroscopy from about two decades ago. A minimum value for the conformal invariance breaking scale is also estimated for the fermiophobic scalar/pseudo-scalar sector to ensure consistency with astrophysics and cosmology. The energy level structure of the Unparticle Uehling shifts are inferred using general methods for the scalar and pseudo-scalar cases and it is shown that the two cases contribute to the energy shifts with the same sign.

hep-ph↗

arXiv2008

Interaction of Dirac and Majorana Neutrinos with Weak Gravitational Fields

In this paper the interaction of high energy neutrinos with weak gravitational fields is briefly explored. The form of the graviton-neutrino vertex is motivated from Lorentz and gauge invariance and the non-relativistic interpretations of the neutrino gravitational form factors are obtained. We comment on the renormalization conditions, the preservation of the weak equivalence principle and the definition of the neutrino mass radius. We associate the neutrino gravitational form factors with specific angular momentum states. Based on Feynman diagrams, spin-statistics, CP invariance and symmetries of the angular momentum states in the neutrino-graviton vertex, we deduce differences between the Majorana and Dirac cases. It is then proved that in spite of the theoretical differences between the two cases, as far as experiments are considered, they would be virtually indistinguishable for any space-time geometry satisfying the weak field condition. We then calculate the transition gravitational form factors for the neutrino by evaluating the relevant Feynman diagrams at 1-loop and estimate a neutrino transition mass radius. The form factor is seen to depend on the momentum transfer very weakly. It is also seen that the neutrino transition mass radius is smaller than the typical neutrino charge radius by a couple of orders of magnitude.

hep-ph↗

arXiv2007

Masses and Mixings in a Grand Unified Toy Model

The generation of the fermion mass hierarchy in the standard model of particle physics is a long-standing puzzle. The recent discoveries from neutrino physics suggests that the mixing in the lepton sector is large compared to the quark mixings. To understand this asymmetry between the quark and lepton mixings is an important aim for particle physics. In this regard, two promising approaches from the theoretical side are grand unified theories and family symmetries. In this note we try to understand certain general features of grand unified theories with Abelian family symmetries by taking the simplest SU(5) grand unified theory as a prototype. We construct an SU(5) toy model with $U(1)_F \otimes Z'_2\otimes Z''_2 \otimes Z'''_2$ family symmetry that, in a natural way, duplicates the observed mass hierarchy and mixing matrices to lowest approximation. The system for generating the mass hierarchy is through a Froggatt-Nielsen type mechanism. One idea that we use in the model is that the quark and charged lepton sectors are hierarchical with small mixing angles while the light neutrino sector is democratic with larger mixing angles. We also discuss some of the difficulties in incorporating finer details into the model without making further assumptions or adding a large scalar sector.

hep-ph↗