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Register a new userAngularly excited and interacting boson stars and Q-balls
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We study angularly excited as well as interacting non-topological solitons, so-called Q-balls and their gravitating counterparts, so-called boson stars in 3+1 dimensions. Q-balls and boson stars carry a non-vanishing Noether charge and arise as solutions of complex scalar field models in a flat space-time background and coupled minimally to gravity, respectively. We present examples of interacting Q-balls that arise due to angular excitations, which are closely related to the spherical harmonics. We also construct explicit examples of rotating boson stars that interact with non-rotating boson stars. We observe that rotating boson stars tend to absorb the non-rotating ones for increasing, but reasonably small gravitational coupling. This is a new phenomenon as compared to the flat space-time limit and is related to the negative contribution of the rotation term to the energy density of the solutions. In addition, our results indicate that a system of a rotating and non-rotating boson star can become unstable if the direct interaction term in the potential is large enough. This instability is related to the appearance of ergoregions.
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We study non-topological solitons, so called Q-balls, which carry a non-vanishing Noether charge and arise as lump solutions of self-interacting complex scalar field models. Explicit examples of new axially symmetric non-spinning Q-ball solutions that have not been studied so far are constructed numerically. These solutions can be interpreted as angular excitations of the fundamental $Q$-balls and are related to the spherical harmonics. Correspondingly, they have higher energy and their energy densities possess two local maxima on the positive z-axis. We also study two Q-balls interacting via a potential term in (3+1) dimensions and construct examples of stationary, solitonic-like objects in (3+1)-dimensional flat space-time that consist of two interacting global scalar fields. We concentrate on configurations composed of one spinning and one non-spinning Q-ball and study the parameter-dependence of the energy and charges of the configuration. In addition, we present numerical evidence that for fixed values of the coupling constants two different types of 2-Q-ball solutions exist: solutions with defined parity, but also solutions which are asymmetric with respect to reflexion through the x-y-plane.
We construct electrically charged Q-balls and boson stars in a model with a scalar self-interaction potential resulting from gauge mediated supersymmetry breaking. We discuss the properties of these solutions in detail and emphasize the differences to the uncharged case. We observe that Q-balls can only be constructed up to a maximal value of the charge of the scalar field, while for boson stars the interplay between the attractive gravitational force and the repulsive electromagnetic force determines their behaviour. We find that the vacuum is stable with respect to pair production in the presence of our charged boson stars. We also study the motion of charged, massive test particles in the space-time of boson stars. We find that in contrast to charged black holes the motion of charged test particles in charged boson star space-times is planar, but that the presence of the scalar field plays a crucial role for the qualitative features of the trajectories. Applications of this test particle motion can be made in the study of extreme-mass ratio inspirals (EMRIs) as well as astrophysical plasmas relevant e.g. in the formation of accretion discs and polar jets of compact objects.
Non-topological solitons such as Q-balls and Q-shells have been studied for scalar fields invariant under global and gauged U(1) symmetries. We generalize this framework to include a Proca mass for the gauge boson, which can arise either from spontaneous symmetry breaking or via the Stuckelberg mechanism. A heavy (light) gauge boson leads to solitons reminiscent of the global (gauged) case, but for intermediate values these Proca solitons exhibit completely novel features such as disconnected regions of viable parameter space and Q-shells with unbounded radius. We provide numerical solutions and excellent analytic approximations for both Proca Q-balls and Q-shells. These allow us to not only demonstrate the novel features numerically, but also understand and predict their origin analytically.
Radially excited $U(1)$ gauged $Q$-balls are studied using both analytical and numerical methods. Unlike the nongauged case, there exists only a finite number of radially excited gauged $Q$-balls at given values of the models parameters. Similarly to the unexcited gauged $Q$-ball, the radially excited one cannot possess the Noether charge exceeding some limiting value. This limiting Noether charge decreases with an increase in the radial excitation of the gauged $Q$-ball. For $n$-th radial excitation, there is a maximum allowable value of the gauge coupling constant, and the existence of the $n$-th radially excited gauged $Q$-ball becomes impossible if the gauge coupling constant exceeds this limiting value. Similarly to the limiting Noether charge, the limiting gauge coupling constant decreases with an increase in the radial excitation. At a fixed Noether charge, the energy of the gauged $Q$-ball increases with an increase in the radial excitation, and thus the radially excited gauged $Q$-ball is unstable against transit into a less excited or unexcited one.
Strings at T ~ T_c are known to be subject to the so-called Hagedorn phenomenon, in which a strings entropy (times T) and energy cancel each other and result in the evolution of the string into highly excited states, or string balls. Intrinsic attractive interaction of strings -- gravitational for fundamental strings or in the context of holographic models of the AdS/QCD type, or sigma exchanges for QCD strings -- can significantly modify properties of the string balls. If heavy enough, those start approaching properties of the black holes. We generate self-interacting string balls numerically, in a thermal string lattice model. We found that in a certain range of the interaction coupling constants they morph into a new phase, the entropy-rich string balls. These objects can appear in the so-called mixed phase of hadronic matter, produced in heavy ion collisions, as well as possibly in the high multiplicity proton-proton or proton-nucleus collisions. Among discussed applications are jet quenching in the mixed phase and also the study of angular deformations of the string balls.
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