Can neutron disappearance/reappearance experiments definitively rule out the existence of hidden braneworlds endowed with a copy of the Standard Model?

International audienceMany works, aiming to explain the origin of dark matter or dark energy, consider the existence of hidden (brane)worlds parallel to our own visible world — our usual Universe — in a multidimensional bulk. Hidden braneworlds allow for hidden copies of the Standard Model. For instance, atoms hidden in a hidden brane could exist as dark matter candidates. As a way to constrain such hypotheses, the possibility for neutron–hidden neutron swapping can be tested thanks to disappearance-reappearance experiments also known as passing-through-walls neutron experiments. The neutron-hidden neutron coupling g can be constrained from those experiments. While g could be arbitrarily small, previous works involving a M4×R1 bulk, with DGP branes, show that g then possesses a value which is reachable experimentally. It is of crucial interest to know if a reachable value for g is universal or not and to estimate its magnitude. Indeed, it would allow, in a near future, to reject definitively — or not — the existence of hidden braneworlds from experiments. In the present paper, we explore this issue by calculating g for DGP branes, for M4×S1/Z2, M4×R2 and M4×T2 bulks. As a major result, no disappearance-reappearance experiment would definitively universally rules out the existence of hidden worlds endowed with their own copy of Standard Model particles, except for specific scenarios with conditions reachable in future experiments

Late baryogenesis in a two-brane universe with a latent CP violation

We introduce a toy model of baryogenesis where our usual visible Universe is a 3-brane coevolving with a hidden 3-brane in a multidimensional bulk, in an ekpyrotic-like approach. The visible matter and antimatter sectors are coupled with the hidden matter and antimatter sectors, breaking the CP invariance and leading to baryogenesis occurring after the quark-gluon era. The issue of leptogenesis is also discussed. This model complements cosmological approaches in which dark matter and dark energy could naturally emerge from many-brane scenarios.Comment: 7 pages, 3 figures, submitte

Sub-GeV-scale signatures of hidden braneworlds up to the Planck scale in a SO(3, 1)-broken bulk

Many-brane universes are at the heart of several cosmological scenarios related to physics beyond the Standard Model. It is then a major concern to constrain these approaches. Two-brane Universes involving $SO(3,1)$-broken 5D bulks are among the cosmological models of interest. They also allow considering matter exchange between branes, a possible way to test these scenarios. Neutron disappearance (reappearance) toward (from) the hidden brane is currently tested with high-precision experiments to constrain the coupling constant $g$ between the visible and hidden neutron sectors. When dealing with the sub-GeV-scale quantum dynamics of fermions, any pair of braneworlds can be described by a non-commutative two-sheeted space-time $M_4\times Z_2$ from which $g$ emerges. Nevertheless, the calculation of the formal link between $g$ for a neutron and $SO(3,1)$-broken 5D bulks remains an open problem until now although necessary to constrain these braneworld scenarios. Thanks to a phenomenological model, we derive $g$ - for a neutron - between the two braneworlds endowed with their own copy of the standard model in a $SO(3,1)$-broken 5D bulk. Constraints on interbrane distance and brane energy scale (or brane thickness) are discussed. While brane energy scale below the GUT scale is excluded, energy scale up to the Planck limit allows neutron swapping detection in forthcoming experiments.Comment: 11 pages, 2 figures, update in references, accepted for publication in International Journal of Modern Physics

New polyvalent low background γ-ray setup at UNamur: Application to S-factor measurements for the 13C(p,γ)14N reaction

The Laboratory of Analysis by Nuclear Reaction (LARN) at the University of Namur (Belgium) is equipped with a low background γ-ray detection system. This setup is made of one ton of lead as passive shielding and plastic scintillators as an anti-cosmic active shielding which covers a large area around a 3.5 × 3.5 inches HPGe detector. This setup makes it possible to reduce the background level from two to three orders of magnitude, depending on the energy range of interest. In this work, this polyvalent detection system is described and used to refine the cross-section measurements of the 13C(p,g)14N nuclear reaction at middle and lowenergies. The reaction 13C(p,g)14N plays an important role in the CNO cycle and s-process in stellar evolution. In this work, we studied more precisely the 13C(p,g)14N ground transition (= 8.06 MeV) for incident energies ranging from 147 to 574.3 keV in the centre-of-mass system generated by the 2 MV Tandetron accelerator ALTAÏS installed at the LARN. Our measurements performed both in reverse (i.e. 1H(13C,g)14N) and direct kinematics are in good agreement with all the data available in the literature, validating our low background detection system.The Laboratory of Analysis by Nuclear Reaction (LARN) at the University of Namur (Belgium) is equipped with a low background γ-ray detection system. This setup is made of one ton of lead as passive shielding and plastic scintillators as anti-cosmic active shielding that covers a large area around a 3.5 × 3.5 in. 2 high purity germanium detector. This setup makes it possible to reduce the background level from two to three orders of magnitude, depending on the energy range of interest. In this work, this polyvalent detection system is described and used to refine the cross-section measurements of the 13C(p,γ) 14N nuclear reaction at middle and low energies. The reaction 13C(p,γ) 14N plays an important role in the carbon-nitrogen-oxygen cycle and s-process in stellar evolution. In this work, we studied more precisely the 13C(p,γ) 14N ground transition (E γ = 8.06 MeV) for incident energies ranging from 147 to 574.3 keV in the center-of-mass system generated by the 2 MV Tandetron accelerator ALTAÏS installed at the LARN. Our measurements performed both in reverse [i.e., 1H( 13C,γ) 14N] and direct kinematics are in good agreement with all the data available in the literature, validating our low background detection system.</p

Conception d’une expérience bas-bruit pour la détection de transitions neutron-neutron caché et recherche de contraintes sur la proximité d’une brane cachée dans le bulk

In many theoretical frameworks our visible world is a 3-brane (a 3-dimensional topological defect) embedded in a multidimensional bulk, possibly coexisting with hidden braneworlds. It is then a major concern to constrain these scenarios,which are at the heart of many scenarios of physics beyond the standard model of particle physics or beyond the cosmological CDM model. In the context of the MURMUR collaboration, the present PhD project will lead to develop and to carry out a neutron passing-through wall experiment, and to explore the theoretical consequences of the experimental results. Indeed, hidden 3-branes can be constrained as matter exchange between braneworlds must occur with a swapping probability p. A neutron n can convert into a hidden neutron n' when scattered by a nucleus with cross section s(n -> n') ~ s(n -> n)p, where s(n -> n) is the usual elastic cross section. Hidden neutrons could, therefore, be generated in the moderator medium of a nuclear research reactor (here the BR2 at the SCK.CEN in Mol), where a high flux of neutrons undergoes many elastic collisions. Being located in another braneworld, these hidden neutrons would interact very weakly with matter and freely escape the reactor out of the biological shielding. However, the reverse swapping process would permit to detect them close to the reactor – with efficiency also proportional to p – thanks to a material able to regenerate hidden neutrons into visible ones. The main part of the present project will consist to develop the ultra-low noise neutron detector, which would allow detecting reappearing neutrons to constrain p and the physics behind. For that purpose, the design of a convenient shielding and of the low-noise neutron detection chain, as well as the required numerical simulations will be necessary. In addition, fundamental theoretical investigations will be considered to constrain existing braneworld scenarios thanks to experimental data.Dans de nombreux travaux théoriques, notre univers visible est une 3-brane (un défaut topologique à 3 dimensions spatiales) au sein d’un espace-temps à plus de 4 dimensions, et coexisterait avec d’autres 3-branes cachées. Il est crucial de contraindre expérimentalement ces modèles au cœur de nombreuses approches au-delà du modèle standard des particules ou du modèle cosmologique Lambda-CDM. Cette thèse vise à mener à bien le projet MURMUR, qui fait l’objet d’une collaboration franco-belge, et qui a pour but de développer et de réaliser une expérience dite de neutrons passe-murailles, et d’explorer les conséquences théoriques des résultats expérimentaux obtenus. Les 3-branes cachées peuvent être contraintes dans la mesure où l’échange de matière entre mondes branaires est possible avec une probabilité d’échange p.Un neutron n peut se transformer en un neutron caché n', lorsqu’il est diffusé par un noyau, avec une section efficace s(n -> n') ~ s(n -> n)p, où s(n -> n) est la section efficace élastique classique. Les neutrons cachés pourraient donc être générés dans le modérateur d’un réacteur nucléaire (dans notre cas le BR2 au SCK.CEN à Mol), où un flux de neutrons élevé subit de nombreuses collisions élastiques. Situés dans un autre monde branaire, les neutrons cachés interagiraient très faiblement avec la matière et s’échapperaient librement du réacteur en évitant le blindage. Par ailleurs, le processus d’échange inverse permettrait de les détecter près du réacteur - avec une efficacité proportionnelle à p - grâce à un matériau capable de régénérer les neutrons cachés en neutrons visibles. L’essentiel du projet consistera donc à développer un détecteur de neutrons à très faible bruit qui permettrait de détecter la réapparition de neutrons pour en contraindre la physique associée. À cette fin, seront nécessaires : la conception d’un blindage et d’une chaîne de détection de neutrons, ainsi que les simulations numériques Monte Carlo requises. De plus, des calculs fondamentaux seront réalisés pour contraindre expérimentalement les scénarios théoriques existants dans la littérature via une approche phénoménologique dont le formalisme mathématique est de la théorie classique du champ

Late baryogenesis in a two-brane universe with a latent CP violation

International audienceWe introduce a toy model of baryogenesis where our usual visible Universe is a 3-brane coevolving with a hidden 3-brane in a multidimensional bulk, in an ekpyrotic-like approach. The visible matter and antimatter sectors are coupled with the hidden matter and antimatter sectors, breaking the CP invariance and leading to baryogenesis occurring after the quark-gluon era. The issue of leptogenesis is also discussed. This model complements cosmological approaches in which dark matter and dark energy could naturally emerge from many-brane scenarios