More Like this

1. Summing inflationary logarithms in nonlinear sigma models

   https://doi.org/10.1007/JHEP03(2022)069  

   Miao, S. P. ; Tsamis, N. C. ; Woodard, R. P. ( March 2022 , Journal of High Energy Physics)

   A bstract We consider two nonlinear sigma models on de Sitter background which involve the same derivative interactions as quantum gravity but without the gauge issue. The first model contains only a single field, which can be reduced to a free theory by a local field redefinition; the second contains two fields and cannot be so reduced. Loop corrections in both models produce large temporal and spatial logarithms which cause perturbation theory to break down at late times and large distances. Many of these logarithms derive from the “tail” part of the propagator and can be summed using a variant of Starobinsky’s stochastic formalism involving a curvature-dependent effective potential. The remaining logarithms derive from the ultraviolet and can be summed using a variant of the renormalization group based on a special class of curvature-dependent renormalizations. Explicit results are derived at 1-loop and 2-loop orders.
2. Quantum Melting of Spin-1 Dimer Solid Induced by Inter-chain Couplings

   Xu, Yi ; Fu, Tianfu ; Hasik, Juraj ; Nevidomskyy, Andriy H. ( September 2022 , arXivorg)

   Dimerized valence bond solids appear naturally in spin-1/2 systems on bipartite lattices, with the geometric frustrations playing a key role both in their stability and the eventual `melting' due to quantum fluctuations. Here, we ask the question of the stability of such dimerized solids in spin-1 systems, taking the anisotropic square lattice with bilinear and biquadratic spin-spin interactions as a paradigmatic model. The lattice can be viewed as a set of coupled spin-1 chains, which in the limit of vanishing inter-chain coupling are known to possess a stable dimer phase. We study this model using the density matrix renormalization group (DMRG) and infinite projected entangled-pair states (iPEPS) techniques, supplemented by the analytical mean-field and linear flavor wave theory calculations. While the latter predicts the dimer phase to remain stable up to a reasonably large interchain-to-intrachain coupling ratio r≲0.6, the DMRG and iPEPS find that the dimer solid melts for much weaker interchain coupling not exceeding r≲0.15. We find the transition into a magnetically ordered state to be first order, manifested by a hysteresis and order parameter jump, precluding the deconfined quantum critical scenario. The apparent lack of stability of dimerized phases in 2D spin-1 systems is indicative of strong quantummore »fluctuations that melt the dimer solid.« less
3. Continuous N\'{e}el-VBS quantum phase transition in non-local one-dimensional systems with SO(3) symmetry

   https://doi.org/10.21468/SciPostPhys.10.2.033  

   Jian, Chao-Ming ; Xu, Yichen ; Wu, Xiao-Chuan ; Xu, Cenke ( January 2021 , SciPost Physics)

   One dimensional (1d) interacting systems with local Hamiltonianscan be studied with various well-developed analytical methods.Recently novel 1d physics was found numerically in systems witheither spatially nonlocal interactions, or at the 1d boundary of2d quantum critical points, and the critical fluctuation in thebulk also yields effective nonlocal interactions at the boundary.This work studies the edge states at the 1d boundary of 2dstrongly interacting symmetry protected topological (SPT) states,when the bulk is driven to a disorder-order phase transition. Wewill take the 2d Affleck-Kennedy-Lieb-Tasaki (AKLT) state as anexample, which is a SPT state protected by the SO(3) spinsymmetry and spatial translation. We found that the original(1+1)d boundary conformal field theory of the AKLT state isunstable due to coupling to the boundary avatar of the bulkquantum critical fluctuations. When the bulk is fixed at thequantum critical point, within the accuracy of our expansionmethod, we find that by tuning one parameter at the boundary,there is a generic direct transition between the long rangeantiferromagnetic Néel order and the valence bond solid (VBS)order. This transition is very similar to the Néel-VBStransition recently found in numerical simulation of a spin-1/2chain with nonlocal spatial interactions. Connections between ouranalytical studies and recent numerical results concerning theedge states of the 2dmore »AKLT-like state at a bulk quantum phasetransition will also be discussed.« less
4. Improved effective dynamics of loop-quantum-gravity black hole and Nariai limit

   https://doi.org/10.1088/1361-6382/ac44a0  

   Han, Muxin ; Liu, Hongguang ( January 2022 , Classical and Quantum Gravity)

   We propose a new model of the spherical symmetric quantum black hole in the reduced phase space formulation. We deparametrize gravity by coupling to the Gaussian dust which provides the material coordinates. The foliation by dust coordinates covers both the interior and exterior of the black hole. After the spherical symmetry reduction, our model is a 1 + 1 dimensional field theory containing infinitely many degrees of freedom. The effective dynamics of the quantum black hole is generated by an improved physical HamiltonianH_Δ. The holonomy correction inH_Δis implemented by the$\overline{\mu }$-scheme regularization with a Planckian area scale Δ (which often chosen as the minimal area gap in loop quantum gravity). The effective dynamics recovers the semiclassical Schwarzschild geometry at low curvature regime and resolves the black hole singularity with Planckian curvature, e.g.R_μνρσR^μνρσ∼ 1/Δ². Our model predicts that the evolution of the black hole at late time reaches the charged Nariai geometry dS₂×S²with Planckian radii$\sim \sqrt{\mathrm{\Delta }}$. The Nariai geometry is stable under linear perturbations but may be unstable by nonperturbative quantum effects. Our model suggests the existence of quantum tunneling of the Nariai geometry and a scenario of black-hole-to-white-hole transition.
5. Atomic-scale tailoring of spin susceptibility via non-magnetic spin-orbit impurities

   https://doi.org/10.1038/s42005-018-0079-3  

   Womack, F. N. ; Adams, P. W. ; Nam, H. ; Shih, C. K. ; Catelani, G. ( November 2018 , Communications Physics)

   Following the discovery of topological insulators, there has been a renewed interest in superconducting systems that have strong spin-orbit (SO) coupling. Here we address the fundamental question of how the spin properties of a otherwise spin-singlet superconducting ground state evolve with increasing SO impurity density. We have mapped out the Zeeman critical field phase diagram of superconducting Al films that were deposited over random Pb cluster arrays of varying density. These phase diagrams give a direct measure of the Fermi liquid spin renormalization, as well as the spin orbit scattering rate. We find that the spin renormalization is a linear function of the average Pb cluster -to- cluster separation and that this dependency can be used to tune the spin susceptibility of the Al over a surprisingly wide range from 0.8χ₀to 4.0χ₀, whereχ₀is the non-interacting Pauli susceptibility.