Grande unification

Résumé

En physique théorique, une théorie de grande unification, encore appelée GUT (pour Grand Unified Theory en anglais) est un modèle de la physique des particules dans lequel les trois interactions de jauge du modèle standard (électromagnétique, nucléaire faible et nucléaire forte) se fusionnent en une seule à hautes énergies. Cette interaction unifiée est caractérisée par une symétrie de jauge plus grande et donc plusieurs vecteurs de force, mais une seule constante de couplage unifiée. Si une Grande Unification est vérifiée dans la nature, alors il est possible que dans le tout début de l'univers il ait existé une ère de grande unification dans laquelle les forces fondamentales ne faisaient qu'une. Dans son état actuel, le modèle standard, bien que très précis, possède néanmoins beaucoup de paramètres libres et en particulier décrit les trois interactions fondamentales précédentes avec trois constantes de couplage différentes. L'unification de la gravité avec les trois autres interac

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https://fr.wikipedia.org/wiki/Grande_unification

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Stochastic gravitational-wave background from metastable cosmic strings

Valerie Fiona Domcke

A metastable cosmic-string network is a generic consequence of many grand unified theories (GUTs) when combined with cosmic inflation. Metastable cosmic strings are not topologically stable, but decay on cosmic time scales due to pair production of GUT monopoles. This leads to a network consisting of metastable long strings on superhorizon scales as well as of string loops and segments on subhorizon scales. We compute for the first time the complete stochastic gravitational-wave background (SGWB) arising from all these network constituents, including several technical improvements to both the derivation of the loop and segment contributions. We find that the gravitational waves emitted by string loops provide the main contribution to the gravitational-wave spectrum in the relevant parameter space. The resulting spectrum is consistent with the tentative signal observed by the NANOGrav and Parkes pulsar timing collaborations for a string tension of G mu similar to 10(-11...-7) and has ample discovery space for ground- and space-based detectors. For GUT-scale string tensions, G mu similar to 10(-8...-7), metastable strings predict a SGWB in the LIGO-Virgo-KAGRA band that could be discovered in the near future.

IOP Publishing Ltd2021

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We interpret the recent NANOGrav results in terms of a stochastic gravitational wave background from metastable cosmic strings. The observed amplitude of a stochastic signal can be translated into a range for the cosmic string tension and the mass of magnetic monopoles arising in theories of grand unification. In a sizable part of the parameter space, this interpretation predicts a large stochastic gravitational wave signal in the frequency band of ground-based interferometers, which can be probed in the very near future. We confront these results with predictions from successful inflation, leptogenesis and dark matter from the spontaneous breaking of a gauged B - L symmetry. (C) 2020 The Authors. Published by Elsevier B.V.

2020

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Supersymmetric hybrid inflation is an exquisite framework to connect inflationary cosmology to particle physics at the scale of grand unification. Ending in a phase transition associated with spontaneous symmetry breaking, it can naturally explain the generation of entropy, matter and dark matter. Coupling F-term hybrid inflation to soft supersymmetry breaking distorts the rotational invariance in the complex inflaton plane - an important fact, which has been neglected in all previous studies. Based on the delta N formalism, we analyze the cosmological perturbations for the first time in the full two-field model, also taking into account the fast-roll dynamics at and after the end of inflation. As a consequence of the two-field nature of hybrid inflation, the predictions for the primordial fluctuations depend not only on the parameters of the Lagrangian, but are eventually fixed by the choice of the inflationary trajectory. Recognizing hybrid inflation as a two-field model resolves two shortcomings often times attributed to it: the fine-tuning problem of the initial conditions is greatly relaxed and a spectral index in accordance with the PLANCK data can be achieved in a large part of the parameter space without the aid of supergravity corrections. Our analysis can be easily generalized to other (including large-field) scenarios of inflation in which soft supersymmetry breaking transforms an initially single-field model into a multi-field model.

Iop Publishing Ltd2014

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