Colossal topological Hall effect at the transition between isolated and lattice-phase interfacial skyrmions

The topological Hall effect is used extensively to study chiral spin textures in various materials. However, the factors controlling its magnitude in technologically-relevant thin films remain uncertain. Using variable-temperature magnetotransport and real-space magnetic imaging in a series of Ir/Fe/Co/Pt heterostructures, here we report that the chiral spin fluctuations at the phase boundary between isolated skyrmions and a disordered skyrmion lattice result in a power-law enhancement of the topological Hall resistivity by up to three orders of magnitude. Our work reveals the dominant role of skyrmion stability and configuration in determining the magnitude of the topological Hall effect.

Two-current correlations in the pion in the Nambu and Jona-Lasinio model

We present an analysis of two-current correlations for the pion in the Nambu–Jona-Lasinio model, with Pauli–Villars regularization. We provide explicit expressions in momentum space for two-current correlations corresponding to the zeroth component of the vector Dirac bilinear in the quark vertices, which has been evaluated on the lattice, thinking to applications in a high energy framework, as a step towards the calculation of pion double parton distributions. The numerical results show a remarkable qualitative agreement with recent lattice data. The factorization approximation into one-body currents is discussed based on previous evaluation of the relevant low energy matrix elements in the Nambu–Jona-Lasinio model, confirming the lattice result.

ON ELECTROWEAK BARYOGENESIS IN THE LITTLEST HIGGS MODEL WITH T-PARITY

We study electroweak baryogenesis within the framework of the littlest Higgs model with T-parity. This model has shown characteristics of a strong first-order electroweak phase transition, which is conducive to baryogenesis in the early Universe. In the T-parity symmetric theory, there are two gauge sectors, viz., the T-even and the T-odd ones. We observe that the effect of the T-parity symmetric interactions between the T-odd and the T-even gauge bosons on gauge-Higgs energy functional is quite small, so that these two sectors can be taken to be independent. The T-even gauge bosons behave like the Standard Model gauge bosons, whereas the T-odd ones are instrumental in stabilizing the Higgs mass. For the T-odd gauge bosons in the symmetric and asymmetric phases and for the T-even gauge bosons in the asymmetric phase, we obtain, using the formalism of Arnold and McLerran, very small values of the ratio (Baryon number violation rate/Universe expansion rate). We observe that this result, in conjunction with the scenario of inverse phase transition in the present work and the value of the ratio obtained from the lattice result of sphaleron transition rate in the symmetric phase, can provide us with a plausible baryogenesis scenario.

SURFACE DIFFUSION AND ANISOTROPIC LATERAL INTERACTIONS

Anisotropic lateral interactions between particles on a rectangular lattice result in anisotropy in the coverage dependence of the chemical diffusion coefficient. This effect is studied in the framework of the lattice-gas model taking into account repulsive lateral interactions in the ground state and also lateral interactions in the activated state. To calculate the diffusion coefficient, the transfer-matrix technique is employed.