Cosmological Constraints on Unparticles as Continuous Mass Scalars

TL;DR

This paper investigates how unparticle models, treated as continuous mass scalars, are constrained by cosmological observations, setting bounds on interaction scales and early universe temperatures.

Contribution

It provides the first detailed cosmological bounds on unparticle interactions modeled as continuous mass scalars with long lifetimes.

Findings

Lower bound on unparticle interaction scale M_U > 20-2600 TeV

Upper bound on early universe temperature as low as 1 TeV

Constraints depend on unparticle dimension d_U and other parameters

Abstract

We study the cosmological constraints on unparticle interactions and the temperature of the Universe for the case where unparticle states can be modelled as continuous mass particles with lifetime > 1s. By considering thermal background quark decay to continuous mass scalars via a scalar operator of dimension d_{U}, we show that the condition that the Universe is not dominated by scalars at nucleosynthesis imposes a lower bound on the scale of the interaction of the unparticle sector, with M_{U} > 20-2600 TeV for \Lambda_{U} > 1 \TeV$, 1.1 < d_{U} < 2.0 and 2 < d_{BZ} < 4. The existence of a long-lived scalar sector also imposes an upper bound on the temperature of the Universe during radiation-domination, which can be as low as a TeV for M_{U} close to its lower bound.