Baryon-symmetric Universe Research Articles

Matter-antimatter asymmetry and dark matter stability from baryon number conservation

There is currently no evidence for a baryon asymmetry in our universe. Instead, cosmological observations have only demonstrated the existence of a quark-antiquark asymmetry, which does not necessarily imply a baryon asymmetric Universe, since the baryon number of the dark sector particles is unknown. In this paper we discuss a framework where the total baryon number of the Universe is equal to zero, and where the observed quark-antiquark asymmetry arises from neutron portal interactions with a dark sector fermion N that carries baryon number. In order to render a baryon symmetric universe throughout the whole cosmological history, we introduce a complex scalar χ, with opposite baryon number and with the same initial abundance as N. Notably, due to the baryon number conservation, χ is absolutely stable and could have an abundance today equal to the observed dark matter abundance. Therefore, in this simple framework, the existence of a quark-antiquark asymmetry is intimately related to the existence (and the stability) of dark matter.

Unified Origin for Visible and Dark Matter in a Baryon-Symmetric Universe from a First-Order Phase Transition

In a baryon-symmetric universe, the baryon asymmetry observed for visible matter is matched by an equal and opposite asymmetry for dark matter, thereby closely connecting the number densities of both types of matter. This is a necessary step towards the goal of explaining the mystery of why the visible and dark matter densities are observed to be similar. In this talk, a way of producing such a universe from bubble nucleation during a first-order phase transition is reviewed. The process is an analog of electroweak baryogenesis.

Affleck-Dine dynamics and the dark sector of pangenesis

Pangenesis is the mechanism for jointly producing the visible and dark matter asymmetries via Affleck-Dine dynamics in a baryon-symmetric universe. The baryon-symmetric feature means that the dark asymmetry cancels the visible baryon asymmetry and thus enforces a tight relationship between the visible and dark matter number densities. The purpose of this paper is to analyse the general dynamics of this scenario in more detail and to construct specific models. After reviewing the simple symmetry structure that underpins all baryon-symmetric models, we turn to a detailed analysis of the required Affleck-Dine dynamics. Both gravity-mediated and gauge-mediated supersymmetry breaking are considered, with the messenger scale left arbitrary in the latter, and the viable regions of parameter space are determined. In the gauge-mediated case where gravitinos are light and stable, the regime where they constitute a small fraction of the dark matter density is identified. We discuss the formation of Q-balls, and delineate various regimes in the parameter space of the Affleck-Dine potential with respect to their stability or lifetime and their decay modes. We outline the regions in which Q-ball formation and decay is consistent with successful pangenesis.Examples of viable dark sectors are presented, and constraints are derived from big bang nucleosynthesis, large scale structure formation and the Bullet cluster. Collider signatures and implications for direct dark matter detection experiments are briefly discussed. The following would constitute evidence for pangenesis: supersymmetry, GeV-scale dark matter mass(es) and a Z′ boson with a significant invisible width into the dark sector.

Visible and dark matter from a first-order phase transition in a baryon-symmetric universe

The similar cosmological abundances observed for visible and dark matter suggest a common origin for both. By viewing the dark matter density as a dark-sector asymmetry, mirroring the situation in the visible sector, we show that the visible and dark matter asymmetries may have arisen simultaneously through a first-order phase transition in the early universe. The dark asymmetry can then be equal and opposite to the usual visible matter asymmetry, leading to a universe that is symmetric with respect to a generalised baryon number. We present both a general structure, and a precisely defined example of a viable model of this type. In that example, the dark matter is ``atomic'' as well as asymmetric, and various cosmological and astrophysical constraints are derived. Testable consequences for colliders include a Z′ boson that couples through the B−L charge to the visible sector, but also decays invisibly to dark sector particles. The additional scalar particles in the theory can mix with the standard Higgs boson and provide other striking signatures.

PANGENESIS: A COMMON ORIGIN FOR VISIBLE AND DARK MATTER

The similar mass densities observed for visible and dark matter in the present-day universe suggest a common origin for both. A scheme called "pangenesis" for realising this using the Affleck-Dine mechanism in a baryon-symmetric universe is presented in this talk.

The search for antihelium in cosmic rays using data from the PAMELA experiment

The generally accepted theory explaining the observed cosmological baryon asymmetry involves mechanisms of baryosynthesis that generate asymmetry in an initially baryon symmetric Universe. Due to the possible inhomogeneous spatial nature of such mechanisms, antimatter domains could arise in the Universe. This hypothesis can be tested by the direct measurement of fluxes of antinuclei in cosmic rays. Searching for antihelium nuclei is therefore among the objectives of the PAMELA experiment. We analyzed data from August 2006 to December 2009 and obtained a preliminary value for the upper limit of the antihelium/helium flux ratio that could lead to some restrictions on the existing theoretical models of the production and propagation of antimatter in the Galaxy.

Antimatter in the Universe

The evidence for cosmologically significant amounts of antimatter in the Universe is reviewed. There is no compelling evidence, either theoretical or experimental, for a baryon-symmetric Universe. The possibility is not completely ruled out, however.

Can we detect antimatter from other galaxies by the use of the Earth's magnetic field and the Moon as an absorber?

We propose a search for antimatter in cosmic rays at energies between 1 and 10 TeV. The electric charge values, including their sign, would be determined by a magnetic analysis combined with an energy measurement. We suggest the use of the Earth's magnetic field, which affordsa bending power of ≈ 100 Tesla x metre. The moon would serve as an absorber, removing, from a given angle of observation, the chemical species of a given energy. The detection of the cosmic rays, together with the measurements of their energy and direction, would be made by Cerenkov calorimetry in the atmosphere. Moonlight would be effectively shielded by the ozone layer with detection of UV light in the range from 0.2 to 0.3 μm. No data exist on antimatter cosmic rays beyond ≈ 10 GeV. The proposed method could reach, in the TeV region, a sensitivity of a few 10 −3 on the {antimatter / total} ratio. Present theoretical evaluations of this ratio for baryon-symmetric Universe models are far above such a sensitivity, while the ratio for antiprotons originating from matter-matter interactions within our Galaxy is expected to be much below.

THE X‐ AND GAMMA‐RAY BACKGROUNDS*

The spectrum of the extragalactic X-ray and gamma-ray backgrounds, originating in a redshift of about 3.0, provides a measurement of the integrated X- and gamma-ray evolution of known sources such as clusters of galaxies, active galaxies, and quasars. It also limits possible new classes of sources, such as accreting black holes and a hot intergalactic medium. Attention is given to the contribution to the X- and gamma-ray backgrounds of known evolved and unevolved sources, as well as the character of small scale and large scale fluctuations in the X-ray background. Speculations as to the origin of the X- and gamma-ray background include such possibilities as the inverse Compton scattering of microwave background photons by intergalactic cosmic-ray electrons, accretion of the intergalactic medium onto pregalactic black holes, and matter-antimatter annihilation in a baryon-symmetric universe.

Cosmological baryon-number domain structure and the first order phase transition of a vacuum

If CP-nonconservation arises from spontaneous symmetry breaking in the very early universe, the universe will have a domain structure of baryon number. We propose a model of the early universe in which domains are stretched exponentially and the radius of the domains is much greater than that of the horizon of the standard big bang model, provided that the grand unified theory undergoes a first order phase transition. If the size of the stretched domains is sufficiently big to avoid pair annihilations of baryon and antibaryon domains, the difficulties of the baryon symmetric universe may be removed.

The first order phase transition of a vacuum and baryon-number domain structure of the universe

If CP-nonconservation arises from spontaneous symmetry breaking in the very early universe, the universe will have a domain structure of baryon number. We propose a model of the early universe in which domains are stretched exponentially and the radius of domains is much greater than that of the standard big bang model, provided that the GUT phase transition is of first order. If the size of the stretched domains is sufficiently big to avoid pair annihilations of baryon and antibaryon domains, the difficulties of the baryon symmetric universe may be removed.

GAMMA‐RAY OBSERVATIONS OF SEYFERT GALAXIES AND THE PROBLEM OF THE EXTRAGALACTIC GAMMA‐RAY BACKGROUND

Annals of the New York Academy of SciencesVolume 336, Issue 1 p. 267-277 GAMMA-RAY OBSERVATIONS OF SEYFERT GALAXIES AND THE PROBLEM OF THE EXTRAGALACTIC GAMMA-RAY BACKGROUND V. Schönfelder, V. Schönfelder Max-Planck-Institut für Physik und Astrophysik Institut für Extraterrestrische Physik 8000 Munich 40 Federal Republic of GermanySearch for more papers by this author V. Schönfelder, V. Schönfelder Max-Planck-Institut für Physik und Astrophysik Institut für Extraterrestrische Physik 8000 Munich 40 Federal Republic of GermanySearch for more papers by this author First published: February 1980 https://doi.org/10.1111/j.1749-6632.1980.tb15935.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume336, Issue1Ninth Texas Symposium on Relativistic AstrophysicsFebruary 1980Pages 267-277 RelatedInformation

Some cosmological consequences of primordial black-hole evaporations

According to Hawking, primordial black holes of less than 10/sup 15/ g would have evaporated by now. This paper examines the way in which small primordial black holes could thereby have contributed to the background density of photons, nucleons, neutrinos, electrons, and gravitons in the universe. Any photons emitted late enough should maintain their emission temperature apart from a redshift effect: it is shown that the biggest contribution should come from primordial black holes of about 10/sup 15/ g, which evaporate in the present era, and it is argued that observations of the ..gamma..-ray background indicate that primordial black holes of this size must have a mean density less than 10/sup -8/ times the critical density. Photons which were emitted sufficiently early to be thermalized could, in principle, have generated the 3 K background in an initially cold universe, but only if the density fluctuations in the early universe had a particular form and did not extend up to a mass scale of 10/sup 15/ g. Primordial black holes of less than 10/sup 14/ g should emit nucleons: it is shown that such nucleons could not contribute appreciably to the cosmic-ray background. However, nucleon emission could have generated the observedmore » number density of baryons in an initially baryon-symmetric universe, provided some CP-violating process operates in black hole evaporations such that more baryons are always produced than antibaryons. We predict the spectrum of neutrinos, electrons, and gravitons which should result from primordial black-hole evaporations and show that the observational limits on the background electron flux might place a stronger limitation on the number of 10/sup 15/ g primordial black holes than the ..gamma..-ray observations. Finally, we examine the limits that various observations place on the strength of any long-range baryonic field whose existence might be hypothesized as a means of preserving baryon number in black-hole evaporations. (AIP)« less