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We examine the commonly explored beyond-standard-model physics scenario of secret neutrino forces, and point out a model prediction that appears to have been overlooked: the generation of unique flavor-changing effects in experiments featuring decay-at-rest (DAR) neutrino sources. These flavor changes occur because the decay that drives neutrino and antineutrino production, $mu^{+}rightarrow e^+ +bar{ u}_{mu}+ u_{e}$, is unique in producing two neutrinos in the final state. Any non-flavor-universal force between the emerging neutrinos would thus induce a new oscillation phase as they escape from each-others potential wells, an effect which is largely absent in experiments that primarily rely on meson decay-in-flight and nuclear decay. We calculate the magnitude of the associated observable and compare it to the anomalous neutrino flavor transformation seen by the LSND experiment, finding a wide but constrained allowed parameter space. We also evaluate existing limits from other experiments, and the testability of this new effect at the future DAR programs JSNS$^2$ and OscSNS.
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We describe a method for sensing short range forces using matter wave interference in dielectric nanospheres. When compared with atom interferometers, the larger mass of the nanosphere results in reduced wave packet expansion, enabling investigations of forces nearer to surfaces in a free-fall interferometer. By laser cooling a nanosphere to the ground state of an optical potential and releasing it by turning off the optical trap, acceleration sensing at the $10^{-8}$m/s$^2$ level is possible. The approach can yield improved sensitivity to Yukawa-type deviations from Newtonian gravity at the $5$ $mu$m length scale by a factor of $10^4$ over current limits.
Neutrinoless double beta decay ($0 ubetabeta$) is a crucial test for lepton number violation. Observation of this process would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. Focussing on so called short-range operators of $0 ubetabeta$ and their potential interplay with the standard light Majorana neutrino exchange, we present the first complete calculation of the relevant nuclear matrix elements, performed within the interacting boson model (IBM-2). Furthermore, we calculate the relevant phase space factors using exact Dirac electron wavefunctions, taking into account the finite nuclear size and screening by the electron cloud. The obtained numerical results are presented together with up-to-date limits on the standard mass mechanism and effective $0 ubetabeta$ short-range operators in the IBM-2 framework. Finally, we interpret the limits in the particle physics scenarios incorporating heavy sterile neutrinos, Left-Right symmetry and R-parity violating supersymmetry.
A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). One of these implies in a lower bound on the effective neutrinoless double beta mass parameter, even for normal hierarchy neutrinos. Here we propose a new model based on the S4 flavor symmetry that leads to the new neutrino mass sum-rule and discuss how to generate a nonzero value for the reactor mixing angle indicated by recent experiments, and the resulting correlation with the solar mixing angle.
DANSS is a highly segmented 1m^3 plastic scintillator detector. Its 2500 scintillator strips have a Gd loaded reflective cover. Light is collected with 3 wave length shifting fibers per strip and read out with 50 PMTs and 2500 SiPMs. The DANSS will be installed under the industrial 3 GW reactor of the Kalinin Nuclear Power Plant at distances varying from 9.7m to 12.2m from the reactor core. Tests of the detector prototype DANSSino demonstrated that in spite of a small size (20x20x100 cm^3) it is quite sensitive to reactor antineutrinos, detecting about 70 Inverse Beta Decay events per day with the signal-to-background ratio of about unity. The prototype tests have demonstrated feasibility to reach the design performance of the DANSS detector. The DANSS experiment will detect about 10 thousand antineutrino events per day with a background below ~1%. Detector will be calibrated every day and its position will be changed frequently to reduce systematic errors. These features will provide a high sensitivity to reactor antineutrino oscillations to sterile neutrinos, suggested recently to explain a so-called reactor anomaly. Data taking will start already next year.
We quantify the effect of gauge bosons from a weakly coupled lepton flavor dependent $U(1)$ interaction on the matter background in the evolution of solar, atmospheric, reactor and long-baseline accelerator neutrinos in the global analysis of oscillation data. The analysis is performed for interaction lengths ranging from the Sun-Earth distance to effective contact neutrino interactions. We survey $sim 10000$ set of models characterized by the six relevant fermion $U(1)$ charges and find that in all cases, constraints on the coupling and mass of the $Z$ can be derived. We also find that about 5% of the $U(1)$ model charges lead to a viable LMA-D solution but this is only possible in the contact interaction limit. We explicitly quantify the constraints for a variety of models including $U(1)_{B-3L_e}$, $U(1)_{B-3L_mu}$, $U(1)_{B-3L_tau}$, $U(1)_{B-frac{3}{2}(L_mu+L_tau)}$, $U(1)_{L_e-L_mu}$, $U(1)_{L_e-L_tau}$, $U(1)_{L_e-frac{1}{2}(L_mu+L_tau)}$. We compare the constraints imposed by our oscillation analysis with the strongest bounds from fifth force searches, violation of equivalence principle as well as bounds from scattering experiments and white dwarf cooling. Our results show that generically, the oscillation analysis improves over the existing bounds from gravity tests for $Z$ lighter than $sim 10^{-8} to 10^{-11}$ eV depending on the specific couplings. In the contact interaction limit, we find that for most models listed above there are values of $g$ and $M_{Z}$ for which the oscillation analysis provides constraints beyond those imposed by laboratory experiments. Finally we illustrate the range of $Z$ and couplings leading to a viable LMA-D solution for two sets of models.
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