The neutrino ground state in a neutron star

We address a recent claim that the stability of neutron stars implies a lower bound on the mass of the neutrino. We argue that the result obtained by some previous authors is due to an improper summation of an infrared-sensitive series and that a non-perturbative "resummation" of the series yields a finite and well-behaved result. The stability of neutron stars thus gives no lower bound on the mass of the neutrino.Comment: 5 pages, 3 figures, Latex (uses espcrc2.sty); contribution to the proceedings of Neutrino 98, Takayama, Japan, 4-9 June, 199

Detecting New Physics in Rare Top Decays at the LHC

In the companion paper it was shown that there are six observables in $gg\to t \bar t \to (b \bar b c) (\bar b \ell \bar \nu)$ that can be used to reveal the presence of new physics (NP) in $t \to b \bar b c$. In the present paper we examine the prospects for detecting and identifying such NP at the LHC, in both the short term and long term. To this end, we develop an algorithm for extracting the NP parameters from measurements of the observables. In the short term, depending on what measurements have been made, there are several different ways of detecting the presence of NP. It may even be possible to approximately determine the values of certain NP parameters. In the long term, it is expected that all six observables will be measured. The values of the NP parameters can then be determined reasonably precisely from a fit to these measurements, which will provide good information about the type of NP present in $t \to b \bar b c$.Comment: Published versio

Disentangling the Seesaw in the Left-Right Model -- An Algorithm for the General Case

Senjanovic and Tello have analyzed how one could determine the neutrino Dirac mass matrix in the minimal left-right model, assuming that the mass matrices for the light and heavy neutrinos could be taken as inputs. They have provided an analytical solution for the Dirac mass matrix in the case that the left-right symmetry is implemented via a generalized parity symmetry and that this symmetry remains unbroken in the Dirac Yukawa sector. We extend the work of Senjanovic and Tello to the case in which the generalized parity symmetry is broken in the Dirac Yukawa sector. In this case the elegant method outlined by Senjanovic and Tello breaks down and we need to adopt a numerical approach. Several iterative approaches are described; these are found to work in some cases but to be highly unstable in others. A stable, prescriptive numerical algorithm is described that works in all but a vanishingly small number of cases. We apply this algorithm to numerical data sets that are consistent with current experimental constraints on neutrino masses and mixings. We also provide some additional context and supporting explanations for the case in which the parity symmetry is unbroken.Comment: 34 pages, 4 figures; published versio

Higgs Sector of the Left-Right Model with Explicit CP Violation

We explore the Higgs sector of the Minimal Left-Right (LR) Model based on the gauge group SU(2)_L x SU(2)_R x U(1)_{B-L} with explicit CP violation in the Higgs potential. Since flavour-changing neutral current experiments and the small scale of neutrino masses both place stringent constraints on the Higgs potential, we seek to determine whether minima of the Higgs potential exist that are consistent with current experimental bounds. We focus on the case in which the right-handed symmetry-breaking scale is only ``moderately'' large, of order 15-50 TeV. Unlike the case in which the Higgs potential is CP-invariant, the CP noninvariant case does yield viable scenarios, although these require a small amount of fine-tuning. We consider a LR model supplemented by an additional U(1) horizontal symmetry, which results in a Higgs sector consistent with current experimental constraints and a realistic spectrum of neutrino masses.Comment: 20 pages, 2 figure