Gauge fields and inflation

The isotropy and homogeneity of the cosmic microwave background (CMB) favors “scalar driven” early Universe inflationary models. However, gauge fields and other non-scalar fields are far more common at all energy scales, in particular at high energies seemingly relevant to inflation models. Hence, in this review we consider the role and consequences, theoretical and observational, that gauge fields can have during the inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main classes of models with gauge fields in the background, models which show violation of the cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.     

A Monte-Carlo generator for statistical hadronization in high energy e+e− collisions

We extend some previous attempts to explain the origin and evolution of primordial magnetic fields during inflation induced from a 5D vacuum. We show that the usual quantum fluctuations of a generalized 5D electromagnetic field cannot provide us with the desired magnetic seeds. We show that special fields without propagation on the extra non-compact dimension are needed to arrive at appreciable magnetic strengths. We also identify a new magnetic tensor field B _ij in this kind of extra dimensional theory. Our results are in very good agreement with observational requirements, in particular from TeV blazars and CMB radiation limits we see that primordial cosmological magnetic fields should be close to scale invariance.     

The search for a primordial magnetic field

Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular, we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude _Bλ$B_{\lambda }$ and the power spectral index _nB$n_B$ and discuss prospects for better determining these quantities in the near future.     

First-principles studies of the magnetic hyperfine field in Fe multilayers

A detailed theoretical study of the magnetic moments and magnetic hyperfine fields in several Fe multilayers (Fe fcc(001)/5X fcc(001), X=Cu and Ag, and Fe bcc(001)/5X fcc(001), X=Ag and Au) as well as in bulk Fe is presented. The calculations have been performed using the spin-polarized, relativistic linear muffin-tin orbital (SPR-LMTO) method of band structure calculation. Therefore, not only the contribution to the hyperfine fields due to the conventional Fermi contact interaction but also due to the spin dipolar and orbital contributions induced by the crystal field and by spin-orbit coupling are accounted for. To decompose the hyperfine field of non-s-electrons into these contributions it has been assumed that they are proportional to the corresponding so-called magnetic dipole moment and the orbital magnetic moment, respectively. In contrast to previous results for pure metals and alloys not only the orbital but also the spin dipolar hyperfine field was found to be non-negligible. The anisotropy of the hyperfine field determined by calculations for in-plane and perpendicular orientation of the magnetisation was found to be very pronounced and closely connected with the corresponding anisotropy of the magnetic dipole moment and the orbital moment.     

强磁场对铝合金中溶质组元分布状态的影响效果

合金中溶质组元的组织形态和分布对于改善合金的组织和性能具有重要意义.本文研究了铝合金在强磁场作用下的凝固行为,考察了Al-Cu，Al-Mg合金中溶质组元的相形态、分布状况随高强度均恒磁场和梯度磁场的强度和方向变化的规律.研究发现，由于Cu元素和Mg元素的物性不同导致其在基体中受到的电磁力不同，在均恒磁场作用下，铝合金中Cu元素和Mg元素在α-Al基体晶粒内和晶界上的分布变化规律相反；在梯度磁场作用下，Cu元素和Mg元素在铝基体中含量和分布状态也有显著的差异.本研究为利用强磁场有效控制不同物性的溶质元素在合金基体中组织状态和分布提供了实验依据. 关键词： 强磁场 铝合金 溶质元素分布 凝固组织 凝固过程     

Magnetogenesis,spectator fields and CMB signatures

A viable class of magnetogenesis models can be constructed by coupling the kinetic term of the hypercharge to a spectator field whose dynamics does not affect the inflationary evolution. The magnetic power spectrum is explicitly related to the power spectrum of (adiabatic) curvature inhomogeneities when the quasi-de Sitter stage of expansion is driven by a single scalar degree of freedom. Depending upon the value of the slow-roll parameters, the amplitude of smoothed magnetic fields over a (comoving) Mpc scale can be as large as 0.01–0.1 nG at the epoch of the gravitational collapse of the protogalaxy. The contributions of the magnetic fields to the Sachs–Wolfe plateau and to the temperature autocorrelations in the Doppler region compare favourably with the constraints imposed by galactic magnetogenesis. Stimulating lessons are drawn on the interplay between magnetogenesis models and their possible CMB signatures.     

New applications of the magnetic X-ray circular dichroism method for surface-magnetism investigations in a photoemission electron microscope

It is shown that magnetic X-ray circular dichroism (MXCD) can be exploited in photoemission electron microscopy not only to visualize the domain structure of ferromagnets, but also to perform quantitative measurements of the stray magnetic fields at the domain boundaries. In the general situation, two MXCD images obtained at different extractor voltages are required. In specific cases, however, it suffices to consider a single image, if it is deformed by the stray magnetic fields compared to a known object geometry. The object geometry means its real shape, scratches or other defects. It is also possible to deposit a paramagnetic film structured in the form of stripes or a grid as a reference on the ferromagnetic sample being investigated. Received: 2 August 2001 / Accepted: 6 September 2001 / Published online: 20 December 2001     

Controlling double vortex states in low-dimensional dipolar systems

The reversal process of the chirality of each opposite vortex belonging to a double vortex state in ferromagnetic hysterons, via the application of in-plane magnetic fields, is reported. Simulations reveal that such a process involves the formation of four intermediate states, including original ones. Hysteresis loops can occur only in a counterclockwise fashion because of one of these intermediate states. Double vortex states can also be controlled by electric fields in ferroelectric nanostructures of different shapes, but with some key differences with respect to the ferromagnetic case.     

Quantum rings in tilted magnetic fields

The electronic states of semiconductor quantum rings (QRs) under tilted magnetic fields are studied in the framework of the effective mass and envelope function approximations. For an axial field, the orbital Zeeman contribution prevails leading to the well-known Aharanov–Bohm spectrum, but it slowly decreases as the magnetic field direction declines. For an in-plane field, only the diamagnetic shift survives and it leads to the formation of double quantum well solutions, this result being relevant for experimental techniques which use in-plane magnetic fields to determine the spin of QR ground states. We also investigate the magnetic response of partially overlapped QRs, which are characteristic of high-density samples of self-assembled rings, and find that the spectrum is quite sensitive to ring coupling.     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostrueture with the periodic magnetic-electric barriers These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostructure with the periodic magnetic-electric barriers. These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers. The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

Mössbauer spectra of magnetic nanoparticles in the model of continuous diffusion and precession of uniform magnetization

A formalism based on the Brown kinetic equation has been developed to describe the Mössbauer spectra of magnetic nanomaterials in the presence of a continuous relaxation process with the inclusion of the diffusion and precession of uniform magnetization in the magnetic-anisotropy field of nanoparticles. Such a generalization of the relaxation model allows not only the inclusion of physical mechanisms of the formation of the magnetic hyperfine structure that are inherent in the system of single-domain magnetic nanoparticles but also an explanation of qualitative features observed in experimental spectra, in particular, the appearance of the magnetic-nature line doublets in these spectra in addition to the standard line sextets of the ⁵⁷Fe nuclei.     

磁爆加载下强磁体的磁场研究

 为了研究磁爆压缩发生器加载下强磁体形成的磁场,对磁爆加载过程进行分析,建立了磁爆加载下强磁体形成磁场的理论模型。按照此模型,对6种不同结构强磁体的磁场进行对比研究,得到了强磁体的磁场变化规律。结果表明：在加载初始阶段,磁爆压缩发生器的自身参数为主要影响因素,各磁体的磁场峰值和范围差别较小;在磁通压缩阶段,电路过程的改变使得磁体结构的影响逐渐显著,各磁体的磁场峰值和范围发生了明显变化;磁体结构对磁场的空间分布具有决定性作用,磁场分布不受加载过程的影响。     

The current status of observational cosmology

Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spear-headed by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galaxies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.     

Spin compensation temperatures induced by longitudinal fields in a mixed spin-3/2 and spin-5/2 Ising ferrimagnet

I studied the ferrimagnetic Ising model with nearest neighbour interactions for a square lattice and simple cubic one, using mean field theory. The free energy of a mixed spin Ising ferrimagnetic model was calculated from a mean field approximation of the Hamiltonian. By minimizing the free energy, I obtained the equilibrium magnetizations and the compensation temperatures. Clear indications of the single-ion anisotropies on the compensation points of the mixed spin-3/2 and spin-5/2 ferrimagnetic lattices are found. Some interesting behaviors of these systems are obtained depending not only on the values of magnetic anisotropies for both sublattice sites but also on the lattice structure. The longitudinal magnetic fields dependence of the spin compensation temperature is the main focus of research. The possibility of many compensation temperatures is indicated.     

Magnetic-field induced spin-Peierls instability in strongly frustrated quantum spin lattices

For a class of frustrated antiferromagnetic spin lattices (in particular, the square-kagomé and kagomé lattices) we discuss the impact of recently discovered exact eigenstates on the stability of the lattice against distortions. These eigenstates consist of independent localized magnons embedded in a ferromagnetic environment and become ground states in high magnetic fields. For appropriate lattice distortions fitting to the structure of the localized magnons the lowering of magnetic energy can be calculated exactly and is proportional to the displacement of atoms leading to a spin-Peierls lattice instability. Since these localized states are present only for high magnetic fields, this instability might be driven by magnetic-field. The hysteresis of the spin-Peierls transition is also discussed.     

Experimental and theoretical studies of the effects of collisions and magnetic fields on quantum beat

The effects of collisions and magnetic fields on quantum beat are treated by the density matrix method. Some experimental quantum beat results of biacetyl in the presence of collisions are presented and theoretically analysed. It is shown that in this case not only pure dephasing but also pressure dependent inherent decay rate constants can be observed; this implies that the Schrödinger method cannot be employed for this case. The magnetic field effect on quantum beat is examined also and it is shown that for the biacetyl molecule magnetic splitting can be observed even in fields of a few gauss.     

On the topology of the adiabatic potential energy surfaces of the H2-ion in a strong magnetic field

The electronic structure of diatomic molecules in strong magnetic fields is investigated by means of the example of the hydrogen molecular ion. A variety of different possibilities for the topological behaviour of the two-dimensional adiabatic electronic potential energy surfaces are derived and discussed. Global as well as local equilibrium configurations of the ion are shown to occur not only for the positions with higher symmetry, i.e. for the parallel and perpendicular positions, but also for configurations which correspond to an inclination of the internuclear axis with respect to the external field.     

Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives

Recent Planck measurements show some CMB anomalies on large angular scales, which confirms the early observations by WMAP. We show that an inflationary model, in which before the slow-roll inflation the Universe is in a superinflationary phase, can generate a large-scale cutoff in the primordial power spectrum, which may account for not only the power suppression on large angular scales, but also a large dipole power asymmetry in the CMB. We discuss an implementation of our model in string theory.     

The nonlocal elastomagnetoelectrostatics of disordered micropolar media

The interactions of electric, magnetic, and elastic subsystems in nonlinear disordered micropolar media that possess a bending–torsion tensor and an nonsymmetric strain tensor have been studied in the framework of phenomenological elastomagnetoelectrostatics. A system of nonlinear equations for determining the ground state of these media has been obtained by the variational method. It is shown that nonuniform external and internal rotations not only create elastic stresses, but also generate additional electric and magnetic fields, while nonuniform elastic stresses and external fields induce internal rotations. The nonlocal character of the micropolar media significantly influences elementary excitations and nonlinear dynamic processes.