On the evolution of global strings in the early universe |
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| Affiliation: | 1. Department of Physics, Presidency College, Chennai 600005 India;2. Department of Nuclear Physics, University of Madras, Chennai 600025, India;1. Laser Science and Technology Centre, Metcalfe House, New Delhi 110054, India;2. Department of Physics, Manav Rachna University, Faridabad, Haryana 121001, India;3. IDDC, Department of Physics, Indian Institute of Technology, New Delhi 110016, India;1. Department of Information Engineering, Padova University, Via Gradenigo 6/B, 35131 Padova, Italy;2. Department of Physics and Astronomy, Padova University, Via Marzolo 8, 35131 Padova, Italy;3. INFN, Padova, Via Marzolo 8, 35131 Padova, Italy;4. State Key Laboratory of Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi''an, China;1. Institute for Nuclear Research of Russian Academy of Sciences, 117312 Moscow, Russia;2. Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia;1. Université Tunis el Manar, Laboratoire de nanomatériaux et des systèmes pour les energies renouvelables, Centre de Recherches et des Technologies de l’Energie, BP95 Hammam Lif, 2050, Tunisia;2. Unité de recherche de Valorisation et Optimisation de l׳Exploitation des Ressources, Faculté des Sciences et Techniques de Sidi Bouzid, Campus Universitaire cité agricole, Université de Kairouan, 9100 Sidi Bouzid, Tunisia;3. Faculté des Sciences de Gafsa, département de Physique, Université de Gafsa, Campus Universitaire, Sidi Ahmed Zarroug, 2112 Gafsa, Tunisia;4. Laboratoire de recherche Energie et Matière pour les Développements des Sciences Nucléaire, Centre National des Sciences et Technologie Nucléaires, 2020 Sidi-Thabet, Tunisia;5. Unité de physique des dispositifs à semi-conducteurs, Faculté des sciences de Tunis, Tunis El Manar University, 2092 Tunis, Tunisia |
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| Abstract: | We find that a bent global string straightens itself out by dissipation into Nambu-Goldstone (NG) bosons in the order of one oscillation time and that the spectrum of radiated NG bosons is 1/k. In the early universe, the assumption that there is one global string per causal horizon is justified after an initial period during which the effect of the primordial plasma on the motion of the strings is non-negligible. We find that the upper bound that axion radiation by strings places on the axion decay constant is comparable to, but not more stringent than the one derived from coherent oscillations of the axion field, i.e. ∫a ≲ 1012GeV. We also discuss the model-dependence of this bound. |
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