Search results for "Weak"
showing 10 items of 1417 documents
Absolute neutrino mass and the Dirac/Majorana distinction from the weak interaction of aggregate matter
2020
The 2$\nu$-mediated force has a range of microns, well beyond the atomic scale. The effective potential is built from the t-channel absorptive part of the scattering amplitude and depends on neutrino properties on-shell. We demonstrate that neutral aggregate matter has a weak charge and calculate the matrix of six coherent charges for its interaction with definite-mass neutrinos. Near the range of the potential the neutrino pair is non-relativistic, leading to observable absolute mass and Dirac/Majorana distinction via different r-dependence and violation of the weak equivalence principle.
Rare weak decays and nuclear structure
2014
Abstract. Weak interactions cause the atomic nuclei to decay via beta and double beta decays. Double beta decays are extremely rare since they are weak-interaction processes of the second order. Also (single) beta decays can be extremely rare. This can be caused by either a large di ff erence between the spins of the initial and final state (the so-called “forbidden” beta decays) or an extremely small Q value (decay energy) of the decay. All these cases are discussed in this article, and particular emphasis is given to the neutrino- less double electron capture on the double beta side of decays. peerReviewed
Self-interacting dark matter and cosmology of a light scalar mediator
2016
We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal. We consider a general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints. The case where dark matter has a self-interaction strength $⟨{\ensuremath{\sigma}}_{V}⟩/{m}_{\ensuremath{\psi}}\ensuremath{\sim}0.1--1\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{g}$ is strongly constrained, in particular by the big bang nucleosynthesis. We show that these constraints can be alleviated by introducing a new light sterile ne…
R-Parity Breaking in Minimal Supergravity
1999
We consider the Minimal Supergravity Model with universality of scalar and gaugino masses plus an extra bilinear term in the superpotential which breaks R-Parity and lepton number. We explicitly check the consistency of this model with the radiative breaking of the electroweak symmetry. A neutrino mass is radiatively induced, and large Higgs-Lepton mixings are compatible with its experimental bound. We also study briefly the lightest Higgs mass. This one-parameter extension of SUGRA-MSSM is the simplest way of introducing R-parity violation.
Perturbative Unitarity Constraints on Charged/Colored Portals
2015
Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak or QCD phase transitions. This implies a new scale of physics and mediator particles needed to facilitate dark matter annihilations. In this work, we consider scenarios where thermal dark matter annihilates via scalar mediators that are colored and/or electrically charged. We show how partial wave unitarity places upper bounds on the masses and couplings on both the dark matter and mediators. To do this, we employ effective field theories with dark matter as well as three flavors of sleptons or squarks with minimum flavor violation. For Dirac (…
Isospin mixing in nuclei within the nuclear density functional theory.
2009
We present the self-consistent, non-perturbative analysis of isospin mixing using the nuclear density functional approach and the rediagonalization of the Coulomb interaction in the good-isospin basis. The largest isospin-breaking effects are predicted for N = Z nuclei and they quickly fall with the neutron excess. The unphysical isospin violation on the mean-field level, caused by the neutron excess, is eliminated by the proposed method. We find a significant dependence of the magnitude of isospin breaking on the parametrization of the nuclear interaction term. A rough correlation has been found between the isospin mixing parameter and the difference of proton and neutron rms radii. The th…
Measurement of the Michel parameters and the nu(tau) helicity in tau lepton decays
2001
A measurement of the Michel parameters and the average $\nu_\tau$ helicity in $\tau$ lepton decays is described. The data was collected with the ALEPH detector at LEP during the years 1991 to 1995. A total integrated luminosity of 155\,$\text{pb}^{-1}$ is analysed. The Michel parameters $\rho_l$, $\xi_l$, $(\xi\delta)_l$ ($l=e,\mu$), and $\eta_\mu$ are determined for the leptonic deca ys, and the chirality parameters $\xi_\pi$, $\xi_\rho$, and $\xi_{a_1}$ for the hadronic final states. Under the assumptions of $e$\bis $\mu$ universality and $\xi_\pi=\xi_\rho=\xi_{a_1}$, the values $\rho_l=0.742\pm 0.016, \eta_l=0.01 2\pm 0.026,\break (\xi\delta)_l=0.776\pm 0.051, \xi_l=0.986\pm 0.074$, and …
Theories relating baryon asymmetry and dark matter
2014
The nature of dark matter and the origin of the baryon asymmetry are two of the deepest mysteries of modern particle physics. In the absence of hints regarding a possible solution to these mysteries, many approaches have been developed to tackle them simultaneously leading to very diverse and rich models. We give a short review where we describe the general features of some of these models and an overview on the general problem. We also propose a diagrammatic notation to label the different models.
Coherent control via weak measurements in P31 single-atom electron and nuclear spin qubits
2018
The understanding of weak measurements and interaction-free measurements has greatly expanded the conceptual and experimental toolbox to explore the quantum world. Here we demonstrate single-shot variable-strength weak measurements of the electron and nuclear spin states of a P31 single-atom donor in silicon. We first show how the partial collapse of the nuclear spin due to measurement can be used to coherently rotate the spin to a desired pure state. We explicitly demonstrate that phase coherence is preserved with high fidelity throughout multiple sequential single-shot weak measurements and that the partial state collapse can be reversed. Second, we use the relation between measurement st…
Falsifying High-Scale Leptogenesis at the LHC
2013
Measuring a non-zero value for the cross section of any lepton number violating (LNV) process would put a strong lower limit on the washout factor for the effective lepton number density in the early universe at times close to the electroweak phase transition and thus would lead to important constraints on any high-scale model for the generation of the observed baryon asymmetry based on LNV. In particular, for leptogenesis models with masses of the right-handed neutrinos heavier than the mass scale observed at the LHC, the implied large washout factors would lead to a violation of the out-of-equilibrium condition and exponentially suppress the net lepton number produced in such leptogenesis…