49 research outputs found
(B-L) Symmetry vs. Neutrino Seesaw
We compute the effective coupling of the Majoron to W bosons at \cO(\hbar)
by evaluating the matrix element of the (B-L) current between the vacuum and a
state. The (B-L) anomaly vanishes, but the amplitude does not vanish
as a result of a UV finite and non-local contribution which is entirely due to
the mixing between left-chiral and right-chiral neutrinos. The result shows how
anomaly-like couplings may arise in spite of the fact that the (B-L) current
remains exactly conserved to all orders in , lending additional support
to our previous proposal to identify the Majoron with the axion.Comment: 13 pages, 1 figure, with additional explanations and clarification
The Minimal Scale Invariant Extension of the Standard Model
We perform a systematic analysis of an extension of the Standard Model that
includes a complex singlet scalar field and is scale invariant at the tree
level. We call such a model the Minimal Scale Invariant extension of the
Standard Model (MSISM). The tree-level scale invariance of the model is
explicitly broken by quantum corrections, which can trigger electroweak
symmetry breaking and potentially provide a mechanism for solving the gauge
hierarchy problem. Even though the scale invariant Standard Model is not a
realistic scenario, the addition of a complex singlet scalar field may result
in a perturbative and phenomenologically viable theory. We present a complete
classification of the flat directions which may occur in the classical scalar
potential of the MSISM. After calculating the one-loop effective potential of
the MSISM, we investigate a number of representative scenarios and determine
their scalar boson mass spectra, as well as their perturbatively allowed
parameter space compatible with electroweak precision data. We discuss the
phenomenological implications of these scenarios, in particular, whether they
realize explicit or spontaneous CP violation, neutrino masses or provide dark
matter candidates. In particular, we find a new minimal scale-invariant model
of maximal spontaneous CP violation which can stay perturbative up to
Planck-mass energy scales, without introducing an unnaturally large hierarchy
in the scalar-potential couplings.Comment: 71 pages, 34 eps figures, numerical error corrected, clarifying
comments adde
The inverse seesaw in conformal electro-weak symmetry breaking and phenomenological consequences
Dual role of cerebral blood flow in regional brain temperature control in the healthy newborn infant.
Small shifts in brain temperature after hypoxia-ischaemia affect cell viability. The main determinants of brain temperature are cerebral metabolism, which contributes to local heat production, and brain perfusion, which removes heat. However, few studies have addressed the effect of cerebral metabolism and perfusion on regional brain temperature in human neonates because of the lack of non-invasive cot-side monitors. This study aimed (i) to determine non-invasive monitoring tools of cerebral metabolism and perfusion by combining near-infrared spectroscopy and echocardiography, and (ii) to investigate the dependence of brain temperature on cerebral metabolism and perfusion in unsedated newborn infants. Thirty-two healthy newborn infants were recruited. They were studied with cerebral near-infrared spectroscopy, echocardiography, and a zero-heat flux tissue thermometer. A surrogate of cerebral blood flow (CBF) was measured using superior vena cava flow adjusted for cerebral volume (rSVC flow). The tissue oxygenation index, fractional oxygen extraction (FOE), and the cerebral metabolic rate of oxygen relative to rSVC flow (CMRO2 index) were also estimated. A greater rSVC flow was positively associated with higher brain temperatures, particularly for superficial structures. The CMRO2 index and rSVC flow were positively coupled. However, brain temperature was independent of FOE and the CMRO2 index. A cooler ambient temperature was associated with a greater temperature gradient between the scalp surface and the body core. Cerebral oxygen metabolism and perfusion were monitored in newborn infants without using tracers. In these healthy newborn infants, cerebral perfusion and ambient temperature were significant independent variables of brain temperature. CBF has primarily been associated with heat removal from the brain. However, our results suggest that CBF is likely to deliver heat specifically to the superficial brain. Further studies are required to assess the effect of cerebral metabolism and perfusion on regional brain temperature in low-cardiac output conditions, fever, and with therapeutic hypothermia