D‐branes in Standard Model building, gravity and cosmology

Abstract

D-branes are by now an integral part of our toolbox towards understanding nature. In this review we will describe recent progress in their use to realize fundamental interactions. The realization of the Standard Model and relevant physics and problems will be detailed. New ideas on realizing 4-dimensional gravity use the brane idea in an important way. Such approaches will be reviewed and compared to the standard paradigm of compactification. Branes can play a pivotal role both in early-and late-universe cosmology mainly via the brane-universe paradigm. Brane realizations of various cosmological ideas (early inflation, sources for dark matter and dark energy, massive gravity etc) will be also reviewed.

Lorentz violation, gravity, dissipation and holography

“…Brane models with a variable speed of light were subsequently constructed by stabilising branes in stable orbits around black branes ( [20] reviewed in the lecture notes [23]; [21,22]). This idea can be brought to its logical conclusion by advocating a planetary brane universe, [23,24].…”

“…This idea can be brought to its logical conclusion by advocating a planetary brane universe, [23,24]. It became also obvious that in orientifold constructions of the standard model (SM), not all SM ingredients emerge from the same D-brane.…”

“…The closest example of a more or less clean separation of a gravitational sector exists in type-II orientifolds in string theory. There, the open string sector that is comprised of D-branes and generates "matter" (The SM is typically embedded in this part, [23,24]) is similar to the QFT sector. There is also the closed string sector that contains among others gravity.…”

Stable non-supersymmetric vacua in the moduli space of non-critical superstrings

“…The Scherk-Schwarz mechanism is a typical example of this property. At weak g s coupling the compactification scale is itself comparable to the string scale which makes it difficult to generate a large separation of scales between m SUSY and m s [5,6]. Supersymmetry breaking at higher loops in perturbation theory or by non-perturbative effects, such as gaugino condensation, instantons etc.…”

“…From the five-dimensional point of view we can write the spacetime supercharges as 5) where α = ±,α = ± and H 2 , H 3 are respectively the bosons bosonizing the worldsheet fermions (ψ X , ψ x 4 ) and (ψ Y , ψ φ ). More details on our conventions and the spacetime supersymmetry algebra can be found in the next section and appendix A.…”