Flavor condensates in brane models and dark energy

Abstract

In the context of a microscopic model of string-inspired foam, in which foamy structures are provided by brany point-like defects (D-particles) in space-time, we discuss flavour mixing as a result of flavour non-preserving interactions of (low-energy) fermionic stringy matter excitations with the defects. Such interactions involve splitting and capture of the matter string state by the defect, and subsequent re-emission. As a result of charge conservation, only electrically neutral matter can interact with the D-particles. Quantum fluctuations of the D-particles induce a nontrivial space-time background; in some circumstances this could be akin to a cosmological Friedman-Robertson Walker expanding-Universe, with weak (but non-zero) particle production. Furthermore the D-particle medium can induce an MSW type effect. We have argued previously, in the context of bosons, that the so-called flavour vacuum is the appropriate state to be used, at least for lowenergy excitations, with energies/momenta up to a dynamically determined cutoff scale. Given the intriguing mass scale provided by neutrino flavour mass differences from the point of view of dark energy, we evaluate the flavour-vacuum expectation value (condensate) of the stress-energy tensor of the 1/2-spin fields with mixing in an effective low-energy Quantum Field Theory in this foaminduced curved space-time. We demonstrate, at late epochs of the Universe, that the fermionic vacuum condensate behaves as a fluid with negative pressure and positive energy; however the equation of state has w fermion > −1/3 and so the contribution of the fermion-fluid flavour vacuum alone could not yield accelerating Universes. Such contributions to the vacuum energy should be considered as (algebraically) additive to the flavoured boson contributions, evaluated in our previous works; this should be considered as natural from (broken) target-space supersymmetry that characterises realistic superstring/supermembrane models of space-time foam. The boson fluid is also characterised by positive energy and negative pressure, but its equation of state is, for late eras, close to w boson → −1, and hence overall the D-foam universe appears accelerating at late eras.

D-foam-induced flavor condensates and breaking of supersymmetry in free Wess-Zumino fluids

“…The equation of state p = wρ (with p pressure and ρ energy density), associated with the flavour vacuum was found to have w = −1 (on using a suitable regularisation). In [2] we claimed that such a behaviour would characterize also the 3+1 dimensional case, in a generic Friedmann-Robertson-Walker (FRW) universe. Moreover, we analyzed a theory with two Dirac fields (complex spin 1/2) on a 3+1 dimensional FRW universe.…”

“…We have, in an earlier work [1,2], investigated the behaviour of an effective vacuum condensate in a field theory arising from a brane model of space-time foam (D-Particle Foam Model ). Within a Brane-World context (cf.…”

“…In our microscopic brane model of [1,2], the seeds of microscopic Lorentz violation are provided by the recoil of D-particles, interacting with flavour matter states. An effective low energy QFT description of this stringy picture needs to reflect this.…”

“…This is in agreement with the general arguments of ref. [5], except that the analysis of the model of [1,2] was done more consistently in a curved background, entailing particle creation and a dynamically generated cut-off scale. However the bosonic and fermionic particles were not considered as part of the same supersymmetric multiplet.…”

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Recently [1,2], we argued that a particular model of string-inspired quantum space-time foam (D-foam) may induce oscillations and mixing among flavoured particles. As a result, rather than the mass-eigenstate vacuum, the correct ground state to describe the underlying dynamics is the flavour vacuum, proposed some time ago by Blasone and Vitiello as a description of quantum field theories with mixing.

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