Cumulative Non-Decoupling Effects of Kaluza-Klein Neutrinos in Electroweak Processes

In Kaluza-Klein theories of low-scale quantum gravity, gravitons and isosinglet neutrinos may propagate in a higher-dimensional space with large compact dimensions, whereas all particles of the Standard Model are confined on a (1+3)-dimensional subspace. After compactification of the extra dimensions, the resulting Yukawa couplings of the Kaluza-Klein neutrinos to the lepton doublets become naturally very suppressed by a higher-dimensional volume factor, in agreement with phenomenological observations. We show that one-loop effects induced by Kaluza-Klein neutrinos, albeit tiny individually, act cumulatively in electroweak processes, giving rise to a non-decoupling behaviour for large values of the higher-dimensional Yukawa couplings. Owing to the non-decoupling effects of Kaluza-Klein neutrinos, we can derive stronger constraints on the parameters of the theory that originate from the non-observation of flavour-violating and universality-breaking phenomena, which involve the W and Z bosons, and the e, $\mu$ and $\tau$ leptons.Comment: 31 pages, LaTeX, to appear in Physical Review

Laboratory Limits on Theories with Sterile Neutrinos in the Bulk

We discuss the phenomenological consequences of theories which describe sterile neutrinos in large extra dimensions, in the so-called bulk. We briefly outline how the cumulative non-decoupling effect due to the tower of Kaluza-Klein singlet neutrinos may equivalently be described by a higher-dimensional effective theory with original order-unity Yukawa couplings. Based on this cumulative phenomenon, we obtain strong constraints on the fundamental quantum gravity scale and/or on the higher-dimensional Yukawa couplings.Comment: 4 pages, to appear in Proc. of the DPF2000 (August 9-12, 2000), Ohio State University, Columbus, Ohio, US

Three Neutrino Oscillations in Uniform Matter

Following similar approaches in the past, the Schrodinger equation for three neutrino propagation in matter of constant density is solved analytically by two successive diagonalizations of 2x2 matrices. The final result for the oscillation probabilities is obtained directly in the conventional parametric form as in the vacuum but with explicit simple modification of two mixing angles ($\theta_{12}$ and $\theta_{13}$) and mass eigenvalues.Comment: presented by Ara Ioannisian at ICHEP2018, Seoul (Conference: C18-07-04

A Standard Model explanation for the MiniBooNE anomaly

We present the results of a new analysis of the data of the MiniBooNE experiment taking into account the additional background of photons. MiniBooNE normalises the rate of photon production to the measured $\pi^0$ production rate. We study neutral current (NC) neutrino-induced $\pi^0$/photon production ($\nu_\mu + A \to \nu_\mu +1\pi^0 / \gamma + X$) on carbon nucleus (A=12). Our conclusion is based on experimental data for photon-nucleus interactions from the A2 collaboration at the Mainz MAMI accelerator. We work in the approximation that decays of the intermediate states (non-resonant N, $\Delta$ resonance, higher resonances) unaffected by its production channel, via photon or Z boson. $1\pi^0+X$ production scales as A$^{2/3}$, the surface area of the nucleus. Meanwhile the photons incoherently created in intermediate states decays will leave the nucleus, and that cross section will be proportional to the atomic number of the nucleus. We also took into account the coherent emission of photons. We show that the new photon background can explain part of the MiniBooNE low-energy excess, thus significantly lowering the number of unexplained MiniBooNE electron-like events from $5.1\sigma$ to $3.6\sigma$.Comment: Contribution to the proceedings of the 40th ICHEP2020, Prague, Czech Republic (Virtual Conference), 6 page

Axion-photon conversion caused by dielectric interfaces: quantum field calculation

Axion-photon conversion at dielectric interfaces, immersed in a near-homogeneous magnetic field, is the basis for the dielectric haloscope method to search for axion dark matter. In analogy to transition radiation, this process is possible because the photon wave function is modified by the dielectric layers ("Garibian wave function") and is no longer an eigenstate of momentum. A conventional first-order perturbative calculation of the transition probability between a quantized axion state and these distorted photon states provides the microwave production rate. It agrees with previous results based on solving the classical Maxwell equations for the combined system of axions and electromagnetic fields. We argue that in general the average photon production rate is given by our result, independently of the detailed quantum state of the axion field. Moreover, our result provides a new perspective on axion-photon conversion in dielectric haloscopes because the rate is based on an overlap integral between unperturbed axion and photon wave functions, in analogy to the usual treatment of microwave-cavity haloscopes.Comment: 15 pages, 2 figures; v2: minor changes to match published versio