The Racah Institute of Physics (Hebrew: מכון רקח לפיסיקה) is an institute at the Hebrew University of Jerusalem, part of the faculty of Mathematics and Natural Sciences on the Edmund J. Safra Campus in the Givat Ram neighborhood of Jerusalem, Israel.The Institute is the center for all research and teaching in the various fields of physics at the Hebrew University. These include astrophysics, high energy physics, quantum physics, nuclear physics, solid state physics, laser and plasma physics, biophysics, non-linear and statistical physics, and nanophysics. Both experimental and theoretical research is carried on in these fields..
Cold, dense streams of gas are predicted to penetrate deeply into massive (greater than or similar to 10(12)M(circle dot)) halos at cosmic noon (z similar to 4-2), fueling galaxies to sustain high star formation rates. We investigate the prevalence of such cold streams in TNG50 over the range z = 4-0, using a novel algorithm to automatically detect cold streams in simulated halos. We qualitatively and quantitatively characterize the geometric and physical properties of the detected streams over cosmic time. We find that cold streams are ubiquitous in massive halos at cosmic noon, occurring in >80% of such systems down to z = 1, before becoming rare by z = 0. At their peak prevalence (z = 2-1), streams are often found in roughly coplanar, three-stream configurations. These streams generally exhibit a dense and cool core, surrounded by a diffuse and warmer envelope. However, we find that, in TNG50, these streams typically disrupt in the outer halo and do not penetrate efficiently to the central galaxy, with the total mass inflow from streams peaking at z = 2. Our results underscore the importance of cold streams in fueling galaxies at early times, but they highlight the need for higher-resolution simulations to fully capture their survival and impact at later epochs. Future cosmological zoom-in simulations, with better resolution in the CGM, will be essential to resolve turbulent mixing layers and feedback-inflow interactions that determine whether cold streams can reach the galactic disk.
The study of chaotic systems, where rare events play a pivotal role, is essential for understanding complex dynamics due to their sensitivity to initial conditions. Recently, tools from large deviation theory, typically applied in the context of stochastic processes, have been used in the study of chaotic systems. Here, we study dynamical observables, A=∑_{n=1}^{N}g(x_{n}), defined along a chaotic trajectory {x_{1},x_{2},...,x_{N}}. For most choices of g(x), A satisfies a central limit theorem: At large sequence size N≫1, typical fluctuations of A follow a Gaussian distribution with a variance that scales linearly with N. Large deviations of A are usually described by the large deviation principle, that is, P(A)∼e^{-NI(A/N)}, where I(a) is the rate function. We find that certain dynamical observables exhibit a remarkable statistical similarity: even when constructed with distinct functions g_{1}(x) and g_{2}(x), different observables are described by the same rate function. We provide a physical interpretation for this striking similarity by showing that g_{1}(x)-g_{2}(x) belongs to a class of functions that we call "derived." Furthermore, we show that if g(x) itself is "derived," then the distribution of A becomes independent of N in the large-N limit and is generally non-Gaussian (although it is mirror-symmetric). We demonstrate that the position observable for certain open maps, used to model random walks and the finite-time Lyapunov exponent for the logistic map are of this derived form, thus providing a simple explanation for some existing results.
In this paper we study Krylov complexity in the presence of single and multiple operators in the DSSYK model, where we can use the analytical techniques coming from chord diagrammatics. One of the results we obtain is that it showcases the switchback effect, when the appropriate “triple-scaling limit” is taken, under which the model becomes dual to semiclassical JT gravity. We build on previous work, where it was shown that, in the continuum limit, Krylov complexity is defined as the sum of expectations value of right and left chord number operators. Here we argue that this property signals the emergence of the geometric nature of this notion of K-complexity. We show that in the regime where DSSYK is dual to semi-classical gravity, the light matter chord corresponds to a shockwave insertion in JT gravity. We identify the geodesic-length dual of the operator complexity and extend the relevant holographic dictionary to describe the details of the matter insertions. Additionally, we define a class of two-sided perturbations of the Lanczos algorithm that allows to analyze the switchback effect. In the appropriate semi-classical limit, this perturbed operator complexity is dual to an ERB length in JT gravity with corresponding shockwave insertions. We thus establish that K-complexity exhibits the expected switchback effect and universal late-time linear growth, consistent with previous findings regarding its geometric nature in the holographic bulk-boundary map.
We investigate pionless effective field theory (π̸EFT) with finite-cutoff regularization as a framework for describing few-nucleon systems. This formulation incorporates effective-range effects already at leading order (LO), thereby reaching next-to-leading-order (NLO) accuracy while maintaining computational efficiency. Using correlated-Gaussian stochastic variational methods in a weak harmonic-oscillator trap, together with neutral and Coulomb-modified quantization conditions, we calculate binding energies and low-energy S-wave scattering parameters for systems with up to five nucleons. At an optimal cutoff, the computed binding energies of the deuteron, triton, helion, and alpha particle reproduce experimental values at the percent level once a three-body force is included. Scattering parameters for proton–proton, nucleon–deuteron, nucleon–triton, proton–helion, deuteron–deuteron, and nucleon–alpha channels are obtained and found to be consistent with both experimental data and existing NLO π̸EFT calculations. These results demonstrate that finite-cutoff π̸EFT offers a robust and predictive framework for few-body nuclear physics.
We investigate how galactic disk structures connect to the detailed properties of their host dark-matter halos using the TNG50 simulation. From the hydrodynamic and matched dark-matter-only runs, we measure a comprehensive list of halo properties describing density structure, angular momentum, shape, assembly history, and environment. Using the morphological decomposition developed in Paper I, we quantify the sizes, scale heights, and mass fractions of the disk components for galaxies at 0 <= z <= 4. A random forest regression shows that halo properties alone predict disk size and thickness with high accuracy, while a symbolic regression (SR) provides compact empirical relations with slightly lower accuracy. Disk height is consistently easier to predict than disk size, and lower-mass halos yield higher accuracy than massive halos. Predictions based on halo properties measured in the hydro simulations outperform those based on halos matched in the dark-matter-only simulation, reflecting the imprint of baryonic restructuring on the inner halo. The SHAP analysis reveals the most informative halo parameters include concentration, Einasto shape, global and inner spin, and recent mass accretion, although their importance varies across disk properties. We show correlations between disk size and the density-profile shape arise primarily from a disk-induced modification of the inner halo, rather than a primordial connection. Finally, we point out that disks become more extended with respect to their host halos at higher redshift in low-mass halos, while massive high-redshift halos show the opposite trend. We provide SR-based prescriptions that accurately map halo properties to disk structures, offering practical tools for galaxy-halo modeling.
