arXiv subjects

S. Fredriksson

Publications and source records attributed to S. Fredriksson.

8 recordsLinked to original sources

arXiv2026

SubTGraph: Large-Scale Subterranean Environment Synthesis with Controllable Topological Variability for Robotic Autonomy Validation

Subterranean (SubT) environments have been a frontier for autonomous robotics, driven by the push for automation of mining operations and the interest in planetary exploration (Martian Lava Tubes). Due to the challenges involved in accessing real SubT environments, rigorous hardening of autonomy stacks in realistic simulation environments is critical. This article fills a well-known gap, which relates to the unavailability of a large-scale simulation-based benchmarking infrastructure for rigorous statistical evaluation of robotic autonomy, due to which it is common for SubT research articles to present validation results in a few environments at best. This article presents SubTGraph, a novel framework for rapid synthesis of multi-level SubT environments with high variability, incorporating user specifications related to topology, dimensionality, textures, etc., to generate distinct environments such as operational mines, natural caves and lava tubes. SubTGraph builds a cost matrix from user-specified structural constraints to guide the classical Dijkstra algorithm to procedurally generate SubT worlds utilizing topometric tiles from the DARPA World Generator. Three robotics case-studies are investigated to demonstrate the utility of SubTGraph for rigorous validation of different layers in the robotic autonomy stack. Structural semantic segmentation is validated against topometric ground truths, multi-agent path planning is widely tested for identification of patterns and trends in the algorithm behavior and LIO SLAM is stress-tested in challenging subterranean sections to identify failure cases. The SubTGraph world creation codebase is open-sourced (https://github.com/LTU-RAI/SubTGraph.git) along with a database consisting of 150 highly variable underground worlds.

cs.RO↗

arXiv2005

The phase diagram of three-flavor quark matter under compact star constraints

The phase diagram of three-flavor quark matter under compact star constraints is investigated within a Nambu--Jona-Lasinio model. Local color and electric charge neutrality is imposed for beta-equilibrated superconducting quark matter. The constituent quark masses and the diquark condensates are determined selfconsistently in the plane of temperature and quark chemical potential. Both strong and intermediate diquark coupling strengths are considered. We show that in both cases, gapless superconducting phases do not occur at temperatures relevant for compact star evolution, i.e., below T ~ 50 MeV. The stability and stucture of isothermal quark star configurations are evaluated. For intermediate coupling, quark stars are composed of a mixed phase of normal (NQ) and two-flavor superconducting (2SC) quark matter up to a maximum mass of 1.21 M_sun. At higher central densities, a phase transition to the three-flavor color flavor locked (CFL) phase occurs and the configurations become unstable. For the strong diquark coupling we find stable stars in the 2SC phase, with masses up to 1.326 M_sun. A second family of more compact configurations (twins) with a CFL quark matter core and a 2SC shell is also found to be stable. The twins have masses in the range 1.301 ... 1.326 M_sun. We consider also hot isothermal configurations at temperature T=40 MeV. When the hot maximum mass configuration cools down, due to emission of photons and neutrinos, a mass defect of 0.1 M_sun occurs and two final state configurations are possible.

hep-ph↗

arXiv2004

Diquark condensation effects on hot quark star configurations

The equation of state for quark matter is derived for a nonlocal, chiral quark model within the mean field approximation.We investigate the effects of a variation of the formfactors of the interaction on the phase diagram of quark matter. Special emphasis is on the occurrence of a diquark condensate which signals a phase transition to color superconductivity and its effects on the equation of state under the condition of beta- equilibrium and charge neutrality. We calculate the quark star configurations by solving the Tolman- Oppenheimer- Volkoff equations and obtain for the transition from a hot, normal quark matter core of a protoneutron star to a cool diquark condensed one a release of binding energy of the order of Delta M c^2 ~ 10^{53} erg. We find that this energy could not serve as an engine for explosive phenomena since the phase transition is not first order. Contrary to naive expectations the mass defect increases when for a given temperature we neglect the possibility of diquark condensation.

nucl-th↗

arXiv1998

Is Dark Matter made up of Massive Quark Objects?

We suggest that dark matter is made up of massive quark objects that have survived from the Big Bang, representing the ground state of ``baryonic'' matter. Hence, there was no overall phase transition of the original quark matter, but only a split-up into smaller objects. We speculate that normal hadronic matter comes about through enforced phase transitions when such objects merge or collide, which also gives rise to the cosmic gamma-ray bursts.

astro-ph↗

arXiv1998

A Quark-Matter Dominated Universe

We present a new scenario for the development of the Universe after the Big Bang, built on the conjecture that a vast majority of the primordial quark matter did not undergo a phase transition to normal nuclear matter, but rather split up into massive quark objects that remained stable. Hence, such primordial quark matter would make up the so-called dark matter. We discuss, mostly in qualitative terms, the consequences for galaxy formation, the origin of normal matter, the occurrence of massive black-holes in galactic centres and the cosmic gamma-ray bursts.

astro-ph↗

arXiv1998

Preon Trinity

We present a new minimal model for the substructure of all known quarks, leptons and weak gauge bosons, based on only three fundamental and stable spin-1/2 preons. As a consequence, we predict three new quarks, three new leptons, and six new vector bosons. One of the new quarks has charge $-4e/3$. The model explains the apparent conservation of three lepton numbers, as well as the so-called Cabibbo-mixing of the $d$ and $s$ quarks, and predicts electromagnetic decays or oscillations between the neutrinos $\barν_μ$ ($ν_μ$) and $ν_e$ ($\barν_e$). Other neutrino oscillations, as well as rarer quark mixings and CP violation can come about due to a small quantum-mechanical mixing of two of the preons in the quark and lepton wave functions.

hep-ph↗

arXiv1997

Gamma-Ray Bursts from Primordial Quark Objects in Space

We investigate the possibility that gamma-ray bursts originate in a concentric spherical shell with a given average redshift and find that this is indeed compatible with the data from the third BATSE (3B) catalog. It is also shown that there is enough freedom in the choice of unknown burst properties to allow even for extremely large distances to the majority of bursts. Therefore, we speculate about an early, and very energetic, origin of bursts, and suggest that they come from phase transitions in massive objects of pure quark matter, left over from the Big Bang.

astro-ph↗

arXiv1997

Higgs Pain? Take a Preon!

The Higgs mechanism is the favourite cure for the main problem with electroweak unification, namely how to reconcile a gauge theory with the need for massive gauge bosons. This problem does not exist in preon models for quark and lepton substructure with composite $Z^0$ and $W$s, which, consequently, also avoid all other theoretical complications and paradoxes with the Higgs mechanism. We present a new, minimal preon model, which explains the family structure, and predicts several new, heavy quarks, leptons and vector bosons. Our preons obey a phenomenological supersymmetry, but without so-called squarks and sleptons, since this SUSY is effective only on the composite scale.

hep-ph↗