Old and New Processes of Vorton Formation

نویسنده

  • Brandon Carter
چکیده

This review is an updated version of a previous very brief overview[1] of the theory of vortons, meaning equilibrium states of cosmic string loops, and of the cosmological processes by which they can be produced in various scenarios. The main innovation here is to draw attention to the possibility of greatly enhanced vorton formation in cases for which the cosmic string current is of the strictly chiral type [2] that arises naturally in certain kinds of supersymmetric field theory. It is rather generally accepted[3] that among the conceivable varieties of topological defects of the vacuum that might have been generated at early phase transitions, the vortex type defects describable on a macrosopic scale as cosmic strings are the kind that is most likely to actually occur – at least in the post inflationary epoch – because the other main categories, namely monopoles and walls, would produce a catastrophic cosmological mass excess. Even a single wall stretching accross a Hubble radius would by itself be too much, while in the case of monopoles it is their collective density that would be too high unless the relevant phase transition occurred at an energy far below that of the G.U.T. level, a possibility that is commonly neglected on the grounds that no monopole formation occurs in the usual models for the transitions in the relevant range, of which the most important is that of electroweak symmetry breaking. The case of cosmic strings is different. One reason is that – although they are not produced in the standard electroweak model – strings are indeed produced at the electroweak level in many of the commonly considered (e.g. supersymmetric) alternative models. A more commonly quoted reason why the case of strings is different, even if they were formed at the G.U.T level, is that – while it may have an important effect in the short run as a seed for galaxy formation – such a string cannot be cosmologically dangerous just by itself, while a distribution of cosmic strings is also cosmologically harmless because (unlike “local” as opposed to “global” monopoles) they will ultimately radiate away all their energy and disappear. However while this latter consideration is indeed valid in the case of ordinary Goto-Nambu type strings, it was pointed out by Davis and Shellard[4] that it need not apply to “superconducting” current-carrying strings of the kind originally introduced by Witten[5]. This is because the occurrence of stable currents allows loops of string to be stabilized in states known as “vortons”, so that they cease to radiate. The way this happens is that the current, whether timelike or spacelike, breaks the Lorentz invariance along the string worldsheet [6, 7, 8, 9], thereby leading to the possibility of rotation, with velocity v say. The centrifugal effect of this rotation, may then

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تاریخ انتشار 1999