Search results for "C.M.M."
showing 10 items of 1066 documents
Masses and magnetic moments of ground-state baryons in covariant baryon chiral perturbation theory
2012
We report on some recent developments in our understanding of the light-quark mass dependence and the SU(3) flavor symmetry breaking corrections to the magnetic moments of the ground-state baryons in a covariant formulation of baryon chiral perturbation theory, the so-called EOMS formulation. We show that this covariant ChPT exhibits some promising features compared to its heavy-baryon and infrared counterparts.
Cosmological searches for a non-cold dark matter component
2017
We explore an extended cosmological scenario where the dark matter is an admixture of cold and additional non-cold species. The mass and temperature of the non-cold dark matter particles are extracted from a number of cosmological measurements. Among others, we consider tomographic weak lensing data and Milky Way dwarf satellite galaxy counts. We also study the potential of these scenarios in alleviating the existing tensions between local measurements and Cosmic Microwave Background (CMB) estimates of the $S_8$ parameter, with $S_8=\sigma_8\sqrt{\Omega_m}$, and of the Hubble constant $H_0$. In principle, a sub-dominant, non-cold dark matter particle with a mass $m_X\sim$~keV, could achieve…
Can interacting dark energy solve the $H_0$ tension?
2017
The answer is Yes! We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant $H_0$ between the Cosmic Microwave Background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two datasets points towards an evidence for a non-zero dark matter-dark energy coupling $\xi$ at more than two standard deviations, with $\xi=-0.26_{-0.12}^{+0.16}$ at $95\%$ CL. However the $H_0$ tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantom-like equation of state $w=-1.184\pm0.…
Constraints on electromagnetic form factors of sub-GeV dark matter from the cosmic microwave background anisotropy
2021
We consider dark matter which have non-zero electromagnetic form factors like electric/magnetic dipole moments and anapole moment for fermionic dark matter and Rayleigh form factor for scalar dark matter. We consider dark matter mass $m_\chi > \cal{ O}({\rm MeV})$ and put constraints on their mass and electromagnetic couplings from CMB and LSS observations. Fermionic dark matter with non-zero electromagnetic form factors can annihilate to $e^+ e^-$ and scalar dark matter can annihilate to $2\gamma$ at the time of recombination and distort the CMB. We analyze dark matter with multipole moments with Planck and BAO observations. We find upper bounds on anapole moment $g_{A}<7.163\times 10^{3} …
(g−2) anomalies and neutrino mass
2020
Motivated by the experimentally observed deviations from standard model predictions, we calculate the anomalous magnetic moments $a_\alpha = (g-2)_\alpha$ for $\alpha=e,\mu$ in a neutrino mass model originally proposed by Babu-Nandi-Tavartkiladze (BNT). We discuss two variants of the model, the original model plus a minimally extended version with an additional hypercharge zero triplet scalar. While the original BNT model can explain $a_\mu$, only the variant with the triplet scalar can explain both experimental anomalies. The heavy fermions of the model can be produced at the high-luminosity LHC and in the part of parameter space, where the model explains the experimental anomalies, it pre…
Dispersion relations in real and virtual Compton scattering
2002
A unified presentation is given on the use of dispersion relations in the real and virtual Compton scattering processes off the nucleon. The way in which dispersion relations for Compton scattering amplitudes establish connections between low energy nucleon structure quantities, such as polarizabilities or anomalous magnetic moments, and the nucleon excitation spectrum is reviewed. We discuss various sum rules for forward real and virtual Compton scattering, such as the Gerasimov-Drell-Hearn sum rule and its generalizations, the Burkhardt-Cottingham sum rule, as well as sum rules for forward nucleon polarizabilities, and review their experimental status. Subsequently, we address the general…
Relativistic corrections to the Drell-Hearn-Gerasimov sum rule in the constitutent quark model
1994
Relativistic corrections have been calculated for the Drell-Hearn-Gerasimov sum rule in the framework of the constituent-quark model. These corrections lead to additional absorption strength due to relativistic dipole currents in the case of a hyperfine interaction. The introduction of anomalous magnetic moments requires a subtraction of the dispersion integral at infinity. The additional effects of such anomalous moments, however, are numerically very small within the model.
Constraining neutrino magnetic moment with solar and reactor neutrino data
2004
We use solar neutrino data to derive stringent bounds on Majorana neutrino transition moments (TMs). Such moments, if present, would contribute to the neutrino-electron scattering cross section and hence alter the signal observed in Super-Kamiokande. Using the latest solar neutrino data, combined with the results of the reactor experiment KamLAND, we perform a simultaneous fit of the oscillation parameters and TMs. Furthermore, we include data from the reactor experiments Rovno, TEXONO and MUNU in our analysis, improving significantly the current constraints on TMs. A comparison with previous works shows that our bounds are the strongest and most general results presented up to now. Finally…
Constraining the neutrino magnetic moment with anti-neutrinos from the Sun
2003
We discuss the impact of different solar neutrino data on the spin-flavor-precession (SFP) mechanism of neutrino conversion. We find that, although detailed solar rates and spectra allow the SFP solution as a sub-leading effect, the recent KamLAND constraint on the solar antineutrino flux places stronger constraints to this mechanism. Moreover, we show that for the case of random magnetic fields inside the Sun, one obtains a more stringent constraint on the neutrino magnetic moment down to the level of \mu_\nu \lsim few \times 10^{-12}\mu_B, similar to bounds obtained from star cooling.
The anomalous magnetic moment of positive and negative muons
1977
Abstract The anomalous g -factor a ≡ ( g −2)/2 has been measured for muons of both charges in the Muon Storage Ring at CERN. The two results, a μ + = 1165910(12) × 10 −9 and a μ − = 1165936(12) × 10 −9 , are in good agreement with each other, and combine to give a mean a μ = 1165922(9) × 10 −9 , which is very close to the most recent theoretical prediction 1165921(10) × 10 −9 . For the experimental results, the total statistical and systematic error is given. The measurements thus confirm the remarkable QED calculation plus hadronic contribution, and serve as a precise verification of the CPT theorem for muons.