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1. Hidden Time Reversal in Driven $XXZ$ Spin Chains: Exact Solutions and New Dissipative Phase Transitions

   https://doi.org/10.1103/PhysRevLett.134.130404  

   Yao, Mingxing; Lingenfelter, Andrew; Belyansky, Ron; Roberts, David; Clerk, Aashish A (April 2025, Physical Review Letters)

   We show that several models of interacting $XXZ$spin chains subject to boundary driving and dissipation possess a subtle kind of time-reversal symmetry, making their steady states exactly solvable. We focus on a model with a coherent boundary drive, showing that it exhibits a unique continuous dissipative phase transition as a function of the boundary drive amplitude. This transition has no analog in the bulk closed system or in incoherently driven models. We also show the steady-state magnetization exhibits a surprising fractal dependence on interaction strength, something previously associated with less easily measured infinite-temperature transport quantities (the Drude weight). Our exact solution also directly yields driven-dissipative double-chain models that have pure, entangled steady states that are current carrying. Published by the American Physical Society2025 

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2. Partially celestial states and their scattering amplitudes

   https://doi.org/10.1103/PhysRevD.109.105020  

   Csáki, Csaba; Telem, Ofri; Terning, John (May 2024, Physical Review D)

   We study representations of the Poincaré group that have a privileged transformation law along a $p$-dimensional hyperplane, and uncover their associated spinor-helicity variables in $D$spacetime dimensions. Our novel representations generalize the recently introduced celestial states and transform as conformal primaries of $SO(p,1)$, the symmetry group of the $p$-hyperplane. We will refer to our generalized states as “partially celestial.” Following Wigner’s method, we find the induced representations, including spin degrees of freedom. Defining generalized spinor-helicity variables for every $D$and $p$, we are able to construct the little group covariant part of partially celestial amplitudes. Finally, we briefly examine the application of the pairwise little group to partially celestial states with mutually nonlocal charges. Published by the American Physical Society2024 

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3. Cyclic Products of Higher-Genus Szegö Kernels, Modular Tensors, and Polylogarithms

   https://doi.org/10.1103/PhysRevLett.133.021602  

   D’Hoker, Eric; Hidding, Martijn; Schlotterer, Oliver (July 2024, Physical Review Letters)

   A wealth of information on multiloop string amplitudes is encoded in fermionic two-point functions known as Szegö kernels. Here we show that cyclic products of any number of Szegö kernels on a Riemann surface of arbitrary genus may be decomposed into linear combinations of modular tensors on moduli space that carry all the dependence on the spin structure $\delta$. The $\delta$-independent coefficients in these combinations carry all the dependence on the marked points and are composed of the integration kernels of higher-genus polylogarithms. We determine the antiholomorphic moduli derivatives of the $\delta$-dependent modular tensors. Published by the American Physical Society2024 

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4. Rationality in four dimensions

   https://doi.org/10.1103/PhysRevD.109.105018  

   Rastelli, Leonardo; Rayhaun, Brandon C (May 2024, Physical Review D)

   By leveraging the physics of the Higgs branch, we argue that the conformal central charges $a$and $c$of an arbitrary 4D $\mathcal{N}=2$superconformal field theory (SCFT) are rational numbers. Our proof of the rationality of $c$is conditioned on a well-supported conjecture about how the Higgs branch of an SCFT is encoded in its protected chiral algebra. To establish the rationality of $a$, we further rely on a widely believed technical assumption on the high-temperature limit of the superconformal index. Published by the American Physical Society2024 

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5. First Measurement of Deeply Virtual Compton Scattering on the Neutron with Detection of the Active Neutron

   https://doi.org/10.1103/PhysRevLett.133.211903  

   Hobart, A; Niccolai, S; Čuić, M; Kumerički, K; Achenbach, P; Alvarado, J S; Armstrong, W R; Atac, H; Avakian, H; Baashen, L; et al (November 2024, Physical Review Letters)

   Measuring deeply virtual Compton scattering (DVCS) on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of generalized parton distributions (GPDs). Neutron targets play a complementary role to transversely polarized proton targets in the determination of the GPD $E$. This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks’ angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the Compton form factors $\mathcal{H}$and $\mathcal{E}$. Published by the American Physical Society2024 

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