Microwave noise in high-T c Josephson junctions

Abstract

We have measured the noise of YBa2Cu3O7−δ superconductor-normal-superconductor (SNS) junctions whose high normal-state resistances and characteristic frequencies make them suitable for THz frequency mixers. By directly measuring the 1 GHz power spectral density delivered to a low-noise 50 Ω radiometer system, the noise could be measured over a wide range of dc voltage and temperature, without complications due to 1/f noise, and without invoking any specific model. At a physical temperature of 4 K, the lowest noise junction had an available noise temperature of 31±2 K, corresponding to an effective noise temperature of the normal resistance of 9 K. The effective noise temperature of the normal resistance is approximately equal to the physical temperature at high temperatures, but approaches a limiting value at low temperatures, implying an excess current noise of unknown origin.

Phenomenological implications of neutrinos in extra dimensions

“…The fact that these two effects could be comparable offers an opportunity to measure CP-violating effects present, if ǫ µτ is complex, as a difference in P (ν µ → ν τ ) from P (ν µ →ν τ ) proportional to L. The CP asymmetry can be maximal with a suitable choice of the pathlength and neutrino energy, if ǫ µτ has a large CP-violating phase [32]. In the minimal model presented in the previous section, the only CP-odd phase is the one present in the neutrino mass matrix (recall that ǫ ij ∝ (m ν m † ν ) ij ), and new CP-violating effects (proportional to L) are suppressed by J CP and by two powers of ǫ:…”

Large gauge invariant nonstandard neutrino interactions

“…For the specific case of a neutrino factory and considering just the purely leptonic NSI under discussion, only effects at the source are relevant, since the detection interactions involve quarks 4 . They are customarily parametrized in terms of ǫ s αβ , which describes an effective source state |ν s α as [4,48,75] …”

“…Since neutrinos have only weak interactions with the SM particles, they may even constitute an excellent window into the new physics underlying the "dark sectors" of the universe, i.e., dark matter and dark energy. Therefore, new physics may very well appear next in the form of exotic couplings involving neutrinos, which are often called non-standard neutrino interactions (NSI) [1][2][3][4][5]. This possibility is being actively explored and will be the subject of the present work.…”

A brief status of non-standard neutrino interactions

“…In the case of production and detection NSIs, neutrino states at sources and detectors can be written as superpositions of pure othonormal flavor eigenstates [15,[18][19][20]:…”