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1. Jets with a Twist: The Emergence of FR0 Jets in a 3D GRMHD Simulation of Zero-angular-momentum Black Hole Accretion

   https://doi.org/10.3847/1538-4357/ad0974  

   Lalakos, Aretaios; Tchekhovskoy, Alexander; Bromberg, Omer; Gottlieb, Ore; Jacquemin-Ide, Jonatan; Liska, Matthew; Zhang, Haocheng (March 2024, The Astrophysical Journal)

   Abstract Spinning supermassive black holes (BHs) in active galactic nuclei magnetically launch relativistic collimated outflows, or jets. Without angular momentum supply, such jets are thought to perish within 3 orders of magnitude in distance from the BH, well before reaching kiloparsec scales. We study the survival of such jets at the largest scale separation to date, via 3D general relativistic magnetohydrodynamic simulations of rapidly spinning BHs immersed into uniform zero-angular-momentum gas threaded by a weak vertical magnetic field. We place the gas outside the BH sphere of influence, or the Bondi radius, chosen to be much larger than the BH gravitational radius,R_B= 10³R_g. The BH develops dynamically important large-scale magnetic fields, forms a magnetically arrested disk (MAD), and launches relativistic jets that propagate well outsideR_Band suppress BH accretion to 1.5% of the Bondi rate, ${\dot{M}}_{\mathrm{B}}$. Thus, low-angular-momentum accretion in the MAD state can form large-scale jets in Fanaroff–Riley (FR) type I and II galaxies. Subsequently, the disk shrinks and exits the MAD state: barely a disk (BAD), it rapidly precesses, whips the jets around, globally destroys them, and lets 5%–10% of ${\dot{M}}_{\mathrm{B}}$reach the BH. Thereafter, the disk starts rocking back and forth by angles 90°–180°: the rocking accretion disk (RAD) launches weak intermittent jets that spread their energy over a large area and suppress BH accretion to ≲2% ${\dot{M}}_{\mathrm{B}}$. Because the BAD and RAD states tangle up the jets and destroy them well insideR_B, they are promising candidates for the more abundant, but less luminous, class of FR0 galaxies. 

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2. Collapsar Black Holes Are Likely Born Slowly Spinning

   https://doi.org/10.3847/2041-8213/ace779  

   Gottlieb, Ore; Jacquemin-Ide, Jonatan; Lowell, Beverly; Tchekhovskoy, Alexander; Ramirez-Ruiz, Enrico (July 2023, The Astrophysical Journal Letters)

   Abstract Collapsing stars constitute the main black hole (BH) formation channel, and are occasionally associated with the launch of relativistic jets that powerγ-ray bursts (GRBs). Thus, collapsars offer an opportunity to infer the natal (before spin-up/down by accretion) BH spin directly from observations. We show that once the BH saturates with a large-scale magnetic flux, the jet power is dictated by the BH spin and mass accretion rate. Core-collapse simulations by Halevi et al. and GRB observations favor stellar density profiles that yield an accretion rate of $\dot{m}\approx {10}^{-2}{M}_{\odot }{\mathrm{s}}^{-1}$, weakly dependent on time. This leaves the spin as the main factor that governs the jet power. By comparing the jet power to characteristic GRB luminosities, we find that the majority of BHs associated with jets are likely born slowly spinning with a dimensionless spin ofa≃ 0.2, ora≃ 0.5 for wobbling jets, with the main uncertainty originating in the unknownγ-ray radiative efficiency. This result could be applied to the entire core-collapse BH population, unless an anticorrelation between the stellar magnetic field and angular momentum is present. In a companion paper, Jacquemin-Ide et al., we show that regardless of the natal spin, the extraction of BH rotational energy leads to spin-down toa≲ 0.2, consistent with gravitational-wave observations. We verify our results by performing the first 3D general-relativistic magnetohydrodynamic simulations of collapsar jets with characteristic GRB energies, powered by slowly spinning BHs. We find that jets of typical GRB power struggle to escape from the star, providing the first numerical indication that many jets fail to generate a GRB. 

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3. Magnetically Driven Neutron-rich Ejecta Unleashed: Global 3D Neutrino–General Relativistic Magnetohydrodynamic Simulations of Collapsars Probe the Conditions for r -process Nucleosynthesis

   https://doi.org/10.3847/2041-8213/adc694  

   Issa, Danat; Gottlieb, Ore; Metzger, Brian D; Jacquemin-Ide, Jonatan; Liska, Matthew; Foucart, Francois; Halevi, Goni; Tchekhovskoy, Alexander (May 2025, The Astrophysical Journal Letters)

   Abstract Collapsars—rapidly rotating stellar cores that form black holes—can power gamma-ray bursts and are proposed to be key contributors to the production of heavy elements in the Universe via the rapid neutron capture process (r-process). Previous neutrino-transport collapsar simulations have been unable to unbind neutron-rich material from the disk. However, these simulations have not included sufficiently strong magnetic fields and the black hole (BH), both of which are essential for launching mass outflows. We presentνh-amr, a novel neutrino-transport general relativistic magnetohydrodynamic (νGRMHD) code, which we use to perform the first 3D globalνGRMHD collapsar simulations. We find a self-consistent formation of a weakly magnetized dense accretion disk, which has sufficient time to neutronize. Eventually, substantial magnetic flux accumulates near the BH, becomes dynamically important, leads to a magnetically arrested disk (MAD), and unbinds some of the neutron-rich material. However, the strong flux also hinders accretion, lowers density, and increases neutrino-cooling timescale, which prevents further disk neutronization. Typical collapsar progenitors with mass accretion rates, $\dot{M}\sim 0.1-1M_{\odot }{\mathrm{s}}^{-1}$, do not produce significant neutron-rich (Y_e < 0.25) ejecta. However, we find that MADs at higher mass accretion rates, $\dot{M}\gtrsim \text{few}{M}_{\odot }{\mathrm{s}}^{-1}$(e.g., for more centrally concentrated progenitors), can unbindM_ej ≲ M_⊙of neutron-rich ejecta. The outflows inflate a shocked cocoon that mixes with the infalling neutron-poor stellar gas and raises the final outflowY_e; however, the finalr-process yield may be determined earlier at the point of neutron capture freeze-out. Future work will explore under what conditions more typical collapsar engines becomer-process factories. 

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4. Leptogenesis during an era of early SU(2) confinement

   https://doi.org/10.1103/nmpt-fwz6  

   Bhalla-Ladd, India; Ginnett, Izzy; Tait, Tim_M P (October 2025, Physical Review D)

   We explore leptogenesis during a cosmological epoch during which the electroweak $\mathrm{SU}(2{)}_L$force is confined. During weak confinement, there is only one conserved nonanomalous global charge, $r$, which is a linear combination of lepton-number, baryon-number, and hypercharge. The inclusion of heavy Majorana neutrinos leads to an $r$-charge and $CP$-violating interaction with a composite scalar, $\mathrm{\Phi }$, and composite fermions, $\mathrm{\Psi }$, allowing for the generation of an $r$-charge asymmetry, which translates into a baryon asymmetry post $\mathrm{SU}(2{)}_L$deconfinement. Determining the resulting baryon asymmetry as a function of the model parameters, we find that the predicted baryon-asymmetry can match observations for a wide swath of parameter space: a weak confinement scale ${\mathrm{\Lambda }}_W\sim {10}^{11}–{10}^{14}\mathrm{GeV}$, the sum of the Standard Model Yukawa couplings $\sum Y_{i\alpha }{Y}_{i\alpha }^{*}\sim {10}^{-2}-{10}^0$, $m_{\mathrm{\Phi }}/m_{\mathrm{\Psi }}\sim 0-0.5$, and a $\mathrm{\Phi }-\mathrm{\Psi }-\mathrm{\Psi }$coupling $\left|g\right|\sim 1$with complex phase ${\theta }_g\sim \pi /4$. While leptogenesis under the assumption of a standard cosmology relies on the complex phase of the neutrino Yukawa couplings, the asymmetry generated in this novel background cosmology primarily depends on a strong phase from $\mathrm{SU}(2{)}_L$confinement, ${\theta }_g$, and favors negligible $CP$-violation in the right-handed neutrino decays. 

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5. Observation of Medium-Induced Yield Enhancement and Acoplanarity Broadening of Low- $p_{\mathrm{T}}$ Jets from Measurements in $pp$ and Central Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.133.022301  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (July 2024, Physical Review Letters)

   The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high $p_{\mathrm{T}}$) hadron trigger in proton-proton and central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter $R=0.2$, 0.4, and 0.5 in the range $7<p_{\mathrm{T},\text{jet}}<140\mathrm{GeV}/c$and trigger-recoil jet azimuthal separation $\pi /2<\mathrm{\Delta }\phi <\pi$. The measurements exhibit a marked medium-induced jet yield enhancement at low $p_{\mathrm{T}}$and at large azimuthal deviation from $\mathrm{\Delta }\phi \sim \pi$. The enhancement is characterized by its dependence on $\mathrm{\Delta }\phi$, which has a slope that differs from zero by $4.7\sigma$. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation. © 2024 CERN, for the ALICE Collaboration2024CERN 

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