Phys. Rev. D 102, 084019 (2020) Spherically symmetric configurations of the non-interacting massive complex
scalar field, representing non-rotating boson stars, are considered within the
framework of ...the modified torsion based $f(T)$ gravity, with $f(T) = T + \alpha
\, T^2/2$. We find that with sufficiently large negative value of $\alpha$ the
mass of the boson stars can be made arbitrarily large. This is in contrast to
General Relativity where an upper bound, $M_{max} \sim M_{Planck}^2/m$, to the
mass of the boson stars built from the non-interacting scalar field exists and
where the masses of boson stars in the astrophysical regime can be obtained
only with the introduction of the scalar field self-interaction. With
sufficiently large negative $\alpha$ we also find negative gravitational
binding energy for all masses, which can be seen as an indication of the
stability of such configurations. In its positive regime, $\alpha$ can not be
made arbitrarily large as a phase transition in the stress--energy components
of the $f(T)$-fluid develops. This phenomenon has already been reported to
occur in polytropic stars constructed within the $f(T)$ gravity theory.
Canonical active Brownian motion Glück, Alexander; Hüffel, Helmuth; Ilijić, Sasa
Physical review. E, Statistical, nonlinear, and soft matter physics,
02/2009, Letnik:
79, Številka:
2 Pt 1
Journal Article
Recenzirano
Odprti dostop
Active Brownian motion is the complex motion of active Brownian particles. They are "active" in the sense that they can transform their internal energy into energy of motion and thus create complex ...motion patterns. Theories of active Brownian motion so far imposed couplings between the internal energy and the kinetic energy of the system. We investigate how this idea can be naturally taken further to include also couplings to the potential energy, which finally leads to a general theory of canonical dissipative systems. Explicit analytical and numerical studies are done for the motion of one particle in harmonic external potentials. Apart from stationary solutions, we study nonequilibrium dynamics and show the existence of various bifurcation phenomena.
We propose an innovative type of ergostats and thermostats for molecular dynamics simulations. A general class of active particle swarm models is considered, where any specific total energy ...(alternatively any specific temperature) can be provided at a fixed point of the evolution of the swarm. We identify the extended system feedback force of the Nosé-Hoover thermostat with the "internal energy" variable of active Brownian motion.
Phys. Rev. D 105, 084020 (2022) In this paper we study properties that the vacuum must possess in the minimal
extension to the teleparallel equivalent of general relativity (TEGR) where the
action is ...supplemented with a quadratic torsion term. No assumption is made
about the weakness of the quadratic term although in the weak-field regime the
validity of our previously derived perturbative solution is confirmed.
Regarding the exact nature of the vacuum, it is found that if the center of
symmetry is to be regular, the mathematical conditions on the tetrad at the
isotropy point mimic those of general relativity. With respect to horizons it
is found that, under very mild assumptions, a smooth horizon cannot exist
unless the quadratic torsion coupling, $\alpha$, vanishes, which is the TEGR
limit (with the Schwarzschild tetrad as its solution). This analysis is then
supplemented with computational work utilizing asymptotically Schwarzschild
boundary data. It is verified that in no case studied does a smooth horizon
form. For $\alpha > 0$ naked singularities occur which break down the equations
of motion before a horizon can form. For $\alpha < 0$ there is a limited range
of $\alpha$ where a vacuum horizon might exist but, if present, the horizon is
singular. Therefore physically acceptable black hole horizons are problematic
in the studied theory at least within the realm of vacuum static spherical
symmetry. These results also imply that static spherical matter distributions
generally must have extra restrictions on their spatial extent and
stress-energy bounds so as to render the vacuum solution invalid in the
singular region and make the solutions finite.
Low-frequency Raman scattering was used to study amorphous solid films of adamantane, a globular non-polar hydrocarbon molecule. As evidenced by its spectral characteristics this type of disorder is ...different from the orientational disorder found in the room temperature plastic phase by the absence of the translational order as well. This gives rise to the boson peak related to acoustic phonons which gradually disappears upon heating with simultaneous emerging of the phonon line at 50
cm
−1 which characterizes the low-temperature ordered phase of adamantane. Adamantane dynamics resembles that of C
60 fullerene although not in the same temperature range. All this makes adamantane an attractive system that could serve as a practical reference in molecular simulation studies of the glassy phase of model fluids.
Spherically symmetric configurations of the non-interacting massive complex scalar field, representing non-rotating boson stars, are considered within the framework of the modified torsion based ...\(f(T)\) gravity, with \(f(T) = T + \alpha \, T^2/2\). We find that with sufficiently large negative value of \(\alpha\) the mass of the boson stars can be made arbitrarily large. This is in contrast to General Relativity where an upper bound, \(M_{max} \sim M_{Planck}^2/m\), to the mass of the boson stars built from the non-interacting scalar field exists and where the masses of boson stars in the astrophysical regime can be obtained only with the introduction of the scalar field self-interaction. With sufficiently large negative \(\alpha\) we also find negative gravitational binding energy for all masses, which can be seen as an indication of the stability of such configurations. In its positive regime, \(\alpha\) can not be made arbitrarily large as a phase transition in the stress--energy components of the \(f(T)\)-fluid develops. This phenomenon has already been reported to occur in polytropic stars constructed within the \(f(T)\) gravity theory.
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