text: 261,47,1384764614412492800,850306776352395265,Mario Reig,"(1/ 5)  New paper today! <LINK> Due to the complexity of the extra-dim. space, String Theory generically suggests the existence of many axion particles, the Axiverse. The number of these particles can be rather large, easily O(100) in most compactifications. (2/5) It is generically believed that some of these axions behave as dark matter (DM) while others might describe our current epoch of accelerated expansion as dynamical dark energy (DE). However, with such a plethora of axions one usually finds... (3/5) .. an overproduction of DM and a picture of DE which is not fully consistent. In this work I show that the same physics that regulates the axion DM overproduction is an excellent candidate to set the initial conditions for a consistent picture of dynamical axion DE. (4/5) The framework offers indications about the maximal temperature that our Universe reached in the past and about its fundamental scale. Also gives hints about the fate of the Universe, it is predicted that it will reenter an era of matter domination after the current epoch. (5/5) Finally and most important, it gives us homework to do: one is challenged to obtain a consistent mechanism of long and low-scale inflation. This is left as an exercise for the reader 😜",https://arxiv.org/abs/2104.09923,"In addition to spectacular signatures such as black hole superradiance and the rotation of CMB polarization, the plenitude of axions appearing in the string axiverse may have potentially dangerous implications. An example is the cosmological overproduction of relic axions and moduli by the misalignment mechanism, more pronounced in regions where the signals mentioned above may be observable, that is for large axion decay constant. In this work, we study the minimal requirements to soften this problem and show that the fundamental requirement is a long period of low-scale inflation. However, in this case, if the inflationary Hubble scale is lower than around $O(100)$ eV, no relic DM axion is produced in the early Universe. Cosmological production of some axions may be activated, via the misalignment mechanism, if their potential minimum changes between inflation and today. As a particular example, we study in detail how the maximal-misalignment mechanism dilutes the effect of dangerous axions and allows the production of axion DM in a controlled way. In this case, the potential of the axion that realises the mechanism shifts by a factor $\Delta\theta=\pi$ between the inflationary epoch and today, and the axion starts to oscillate from the top of its potential. We also show that axions with masses $m_a\sim O(1-100)\, H_0$ realising the maximal-misalignment mechanism generically behave as dark energy with a decay constant that can take values well below the Planck scale, avoiding problems associated to super-Planckian scales. Finally, we briefly study the basic phenomenological implications of the mechanism and comment on the compatibility of this type of maximally-misaligned quintessence with the swampland criteria. ",The Stochastic Axiverse,5,"['(1/ 5)   New paper today!\n\n<LINK>\n\nDue to the complexity of the extra-dim. space, String Theory generically suggests the existence of many axion particles, the Axiverse. The number of these particles can be rather large, easily O(100) in most compactifications.', '(2/5) It is generically believed that some of these axions behave as dark matter (DM) while others might describe our current epoch of accelerated expansion as dynamical dark energy (DE). However, with such a plethora of axions one usually finds...', '(3/5) ..  an overproduction of DM and a picture of DE which is not fully consistent. In this work I show that the same physics that regulates the axion DM overproduction is an excellent candidate to set the initial conditions for a consistent picture of dynamical axion DE.', '(4/5) The framework offers indications about the maximal temperature that our Universe reached in the past and about its fundamental scale. Also gives hints about the fate of the Universe, it is predicted that it will reenter an era of matter domination after the current epoch.', '(5/5) Finally and most important, it gives us homework to do: one is challenged to obtain a consistent mechanism of long and low-scale inflation. This is left as an exercise for the reader 😜']",21,04,1250