arXiv subjects

Isaac G. Smith

Publications and source records attributed to Isaac G. Smith.

5 recordsLinked to original sources

arXiv2026

The O(4)-breaking bubble

False vacuum decay in field theory is thought to be dominated by Coleman's O(4)-symmetric bounce, the minimum action nontrivial solution of the imaginary time equations of motion. Beyond the bounce, non-constructive existence proofs of O(4)-breaking solutions are available in the mathematics literature, but the solutions themselves, and their physics, have remained unknown. Considering the simple, bounded-below, scalar field potential $V(\phi)=\frac{m^2}{2}\phi^2-\frac{\lambda}{4}\phi^4+\frac{g}{6}\phi^6$, we construct a nonradial solution explicitly: two bubble-tubes of opposite sign wrapping orthogonal rings, invariant under ${\rm O}(2)\times{\rm O}(2)$ rotations combined with a parity that exchanges the rings. The solution admits valid Cauchy data for real time evolution from a $t=0$ slice, and supports an odd number of unstable deformation modes.

hep-th↗

arXiv2026

Corrections to the Smoothness and On-Shell Approximations in Femtoscopy and Coalescence

Relativistic heavy-ion collisions produce femtometer-scale sources whose space-time structure can be constrained using two-particle femtoscopic correlations. Standard implementations rely on the smoothness and on-shell approximations, which effectively remove the relative momentum dependence of the particle emission function. We explore the validity of these approximations by deriving model-independent expansions that quantify the leading corrections for femtoscopy and coalescence with arbitrary sources and final-state interactions. The resulting first- and second-order correction terms can be evaluated with essentially the same numerical complexity as the usual Koonin-Pratt expressions; for angle-averaged correlations the first-order contributions vanish by symmetry. We illustrate the framework with explicit calculations in a blast-wave source model; for blast-wave parameter sets representative of pp and PbPb fits at LHC energies, the corrections are at or below the percent level for pp correlations and deuteron coalescence. These corrections are potentially subdominant compared to other effects, for example, corrections to the equal time approximation.

nucl-th↗

arXiv2025

Introducing STARDIS: An Open and Modular Stellar Spectral Synthesis Code

We introduce a new 1D stellar spectral synthesis Python code called stardis. stardis is a modular, open-source radiative transfer code that is capable of spectral synthesis from near-UV to IR for FGK stars. We describe the structure, inputs, features, underlying physics, and assumptions of stardis as well as the radiative transfer scheme implemented. To validate our code, we show spectral comparisons between stardis and korg with the same input atmospheric structure models, and also compare qualitatively to phoenix for solar models. We find that stardis generally agrees well with korg for solar models on the few percent level or better, that the codes can diverge in the ultraviolet, with more extreme differences in cooler stars. stardis can be found at https://github.com/tardis-sn/stardis, and documentation can be found at https://tardis-sn.github.io/stardis/.

astro-ph.SR↗

arXiv2025

In-Medium Similarity Renormalization Group at Finite Temperature

The study of nuclei at finite temperature is of immense interest for many areas of nuclear astrophysics and nuclear-reaction science. A variety of ab initio methods are now available for computing the properties of nuclei from interactions rooted in Quantum Chromodynamics, but applications have largely been limited to zero temperature. In the present work, we extend one such method, the In-Medium Similarity Renormalization Group (IMSRG), to finite temperature. Using an exactly-solvable schematic model that captures essential features of nuclear interactions, we show that the FT-IMSRG can accurately determine the energetics of nuclei at finite temperature, and we explore the accuracy of the FT-IMSRG in different parameter regimes, e.g., strong and weak pairing. In anticipation of FT-IMSRG applications for finite nuclei and infinite matter, we discuss differences arising from the choice of working with the canonical and the grand canonical ensembles. In future work, we will apply the FT-IMSRG with realistic nuclear interactions to compute nuclear structure and reaction properties at finite temperature, which are important ingredients for understanding nucleosynthesis in stellar environments, or modeling reactions of hot compound nuclei.

nucl-th↗

arXiv2023

StaNdaRT: A repository of standardized test models and outputs for supernova radiative transfer

We present the first results of a comprehensive supernova (SN) radiative-transfer (RT) code-comparison initiative (StaNdaRT), where the emission from the same set of standardized test models is simulated by currently-used RT codes. A total of ten codes have been run on a set of four benchmark ejecta models of Type Ia supernovae. We consider two sub-Chandrasekhar-mass ($M_\mathrm{tot} = 1.0$ M$_\odot$) toy models with analytic density and composition profiles and two Chandrasekhar-mass delayed-detonation models that are outcomes of hydrodynamical simulations. We adopt spherical symmetry for all four models. The results of the different codes, including the light curves, spectra, and the evolution of several physical properties as a function of radius and time, are provided in electronic form in a standard format via a public repository. We also include the detailed test model profiles and several python scripts for accessing and presenting the input and output files. We also provide the code used to generate the toy models studied here. In this paper, we describe in detail the test models, radiative-transfer codes and output formats and provide access to the repository. We present example results of several key diagnostic features.

astro-ph.SR↗