Search results for "MAGNETIC DIPOLE"
showing 10 items of 217 documents
Singlet-groundstate magnetism in TbP
1979
Elastic neutron scattering and magnetic susceptibility data are reported for temperatures around the Neel-point,TN=7.3 K, and for zero magnetic field. AboveTN, the temperature dependence of the magnetic central peak intensity can adequately be described within the RPA assuming isotropic exchange between nearest and next-nearest neighbours as the only parameters. This two-parameter model is quantitatively confirmed by the susceptibility data. AtTN, magnetic Bragg-intensities arise almost discontinuously (reaching 70% of the saturation within 0.1 K) accompanied by thermal hysteresis. For all temperatures belowTN the sublattice magnetic moment is explained by solutions of meanfield equations, …
Effects of the magnetodipolar interactions in the alternating magnetic fields
1999
A macroscopic theory for the description of the structure formation in a system of magnetic dipoles under the action of a high-frequency rotating field is presented. Continuum equations for the effective magnetic field strength describing particle interactions are derived. It is shown that, contrary to the case of a constant magnetic field, where the demagnetizing field arising from a concentration fluctuation stabilizes the system with respect to the phase separation, the same concentration fluctuation will be amplified in the case of a rotating magnetic field, leading to the formation of a layered structure. The extensions of the model necessary for the description of the formation of the…
An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment
2001
We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e+ e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment the next-to-leading order results related to the vacuum polarization function are accurately re…
Review of dark photon searches
2016
Dark Photons are hypothetical extra-U(1) gauge bosons, which are motivated by a number of astrophysical anomalies as well as the presently seen deviation between the Standard Model prediction and the direct measurement of the anomalous magnetic moment of the muon, (g − 2)μ . The Dark Photon does not serve as the Dark Matter particle itself, but acts as a messenger particle of a hypothetical Dark Sector with residual interaction to the Standard Model. We review recent Dark Photon searches, which were carried out in a global effort at various hadron and particle physics facilities. We also comment on the perspectives for future invisble searches, which directly probe the existence of Light Da…
Lattice QCD and the timelike pion form factor.
2011
We present a formula that allows one to calculate the pion form factor in the timelike region 2mpi <= sqrt{s} <= 4mpi in lattice QCD. The form factor quantifies the contribution of two-pion states to the vacuum polarization. It must be known very accurately in order to reduce the theoretical uncertainty on the anomalous magnetic moment of the muon. At the same time, the formula constitutes a rare example where, in a restricted kinematic regime, the spectral function of a conserved current can be determined from Euclidean observables without an explicit analytic continuation.
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} …
LHC as an Axion Factory: Probing an Axion Explanation for (g−2)μ with Exotic Higgs Decays
2017
We argue that a large region of so-far unconstrained parameter space for axionlike particles (ALPs), where their couplings to the standard model are of order (0.01-1) TeV^{-1}, can be explored by searches for the exotic Higgs decays h→Za and h→aa in run 2 of the LHC. Almost the complete region in which ALPs can explain the anomalous magnetic moment of the muon can be probed by searches for these decays with subsequent decay a→γγ, even if the relevant couplings are loop suppressed and the a→γγ branching ratio is less than 1.
Testing the Standard Model at the precision frontier: the anomalous magnetic moment of the muon
2014
The anomalous magnetic moment of the muon (g − 2)μ is one of the most precisely measured quantities in particle physics (0.54 ppm). There is a long-standing discrepancy of 3-4 standard deviations between the direct measurement of (g − 2)μ and its theoretical evaluation. This theoretical prediction is subdivided into three contributions: QED, weak and hadronic. The QED and weak parts can be determined in perturbative approaches with very high precision. Thus, the hadronic uncertainty dominates the total theoretical uncer- tainty. Within the hadronic uncertainty, the largest contribution stems from the vacuum polarization term, which can be evaluated with the measurement of the inclusive hadr…
Minimal Leptoquark Explanation for theRD(*),RK, and(g−2)μAnomalies
2016
We show that by adding a single new scalar particle to the standard model, a TeV-scale leptoquark with the quantum numbers of a right-handed down quark, one can explain in a natural way three of the most striking anomalies of particle physics: the violation of lepton universality in B[over ¯]→K[over ¯]l^{+}l^{-} decays, the enhanced B[over ¯]→D^{(*)}τν[over ¯] decay rates, and the anomalous magnetic moment of the muon. Constraints from other precision measurements in the flavor sector can be satisfied without fine-tuning. Our model predicts enhanced B[over ¯]→K[over ¯]^{(*)}νν[over ¯] decay rates and a new-physics contribution to B_{s}-B[over ¯]_{s} mixing close to the current central fit v…
Hadronic inputs to the (g– 2)μpuzzle
2016
There is a long standing discrepancy of 3 – 4 standard deviations between the direct measurement and the Standard Model prediction of the anomalous magnetic moment of the muon (g – 2) μ . While new direct measurements have been proposed to clarify the situation, theory calculations are completely limited by the accuracy of the hadronic contributions to (g – 2) μ . In order to increase their precision, experimental information can be used as input. In this presentation we will discuss recent and future measurements of relevant hadronic cross sections and transition form factors.