arXiv subjects

Dor Ben-Amotz

Publications and source records attributed to Dor Ben-Amotz.

4 recordsLinked to original sources

arXiv2026

Shape Shifting Light Dark Matter Solitons

Dark matter consisting of a Bose-Einstein condensate (BEC) of ultralight particles forms solitons whose cored shape becomes increasingly cusped under the influence of a central point mass, such as a supermassive black hole. Here we present a unified analytic description of the resulting shape changes as a function of soliton mass fraction, spanning the hydrogenic to self-gravitating soliton limits. Solutions of the Schrödinger-Poisson equation are expressed as a sum of five Gaussians with numerically optimised coefficients, yielding closed-form expressions for soliton shape-dependent properties. Moreover, new mass-fraction-dependent scaling relations are used to approximate soliton size, density, and total mass directly in terms of observed stellar velocity dispersion and half-light radius. Applications to dwarf spheroidal (dSph) and ultra-faint dwarf (UFD) galaxies -- validated using a spherical-isotropic Jeans analysis -- show that the observed stellar density, velocity and enclosed mass are consistent either with dSph and UFD galaxies having different ultralight dark matter particle masses and no black holes, or with a single universal ultralight dark matter particle mass, requiring the presence of supermassive black holes in many UFD galaxies. These results, combined with a more detailed analysis of the radially resolved stellar velocity dispersions of Draco (dSph) and Segue~I (UFD), are found to be consistent with a universal ultralight dark matter particle mass of $m_0 \approx 1.5\times 10^{-22}$\,eV/c$^2$, to within a factor of~2. The results demonstrate the utility of soliton shape-shifting predictions in constraining dwarf galaxy dark matter profiles and revealing the possible presence of central black holes.

astro-ph.GA↗

arXiv2019

Hiding in the crowd: Spectral signatures of overcoordinated hydrogen bond environments

Molecules with an excess number of hydrogen-bonding partners play a crucial role in fundamental chemical processes, ranging from the anomalous diffusion in supercooled water to the transport of aqueous proton defects and the ordering of water around hydrophobic solutes. Here we show that overcoordinated hydrogen bond environments can be identified in both the ambient and supercooled regimes of liquid water by combining experimental Raman multivariate curve resolution measurements and machine learning accelerated quantum simulations. In particular, we find that OH groups appearing in spectral regions usually associated with non-hydrogen-bonded species actually correspond to hydrogen bonds formed in overcoordinated environments. We further show that only these species exhibit a turnover in population as a function of temperature, which is robust and persists under both constant pressure and density conditions. This work thus provides a new tool to identify, interpret, and elucidate the spectral signatures of crowded hydrogen bond networks.

physics.chem-ph↗

arXiv2017

The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.

physics.chem-ph↗

arXiv2006

The Rectified Second Law of Thermodynamics

Equilibrium thermodynamics is combined with Jarzynski's irreversible work theorem to quantify the excess entropy produced by irreversible processes. The resulting rectified form of the second law parallels the first law, in the sense that it facilitates the experimental measurement of excess entropy changes resulting from irreversible work and heat exchanges, just as the first law quantifies energy changes produced by either reversible or irreversible work and heat exchanges. The general form of the rectified second law is further applied to a sub-class of quasi-static irreverisble (QSI) processes, for which all the thermodynamic functions of both the system and surroundings remain continuously well-defined, thus facilitating excess entropy measurements by integrating exact differential functions along QSI paths. The results are illustrated by calculating the mechanical and thermal excess entropy produced by the irreversible unfolding of an RNA molecule.

cond-mat.stat-mech↗