20 research outputs found
Gravitational wave and collider implications of electroweak baryogenesis aided by non-standard cosmology
We consider various models realizing baryogenesis during the electroweak phase transition (EWBG). Our focus is their possible detection in future collider experiments and possible observation of gravitational waves emitted during the phase transition. We also discuss the possibility of a non-standard cosmological history which can facilitate EWBG. We show how acceptable parameter space can be extended due to such a modification and conclude that next generation precision experiments such as the ILC will be able to confirm or falsify many models realizing EWBG. We also show that, in general, collider searches are a more powerful probe than gravitational wave searches. However, observation of a deviation from the SM without any hints of gravitational waves can point to models with modified cosmological history that generically enable EWBG with weaker phase transition and thus, smaller GW signals
Initial conditions for inflation
Within the α-attractors framework we investigate scalar potentials with the same pole as the one featured in the kinetic term. We show that, in field space, this leads to directions without a plateau. Using this, we present a proposal, which manages to overcome the initial conditions problem of inflation with a plateau. An earlier period of proto-inflation, beginning at Planck scale, accounts for the Universe expansion and arranges the required initial conditions for inflation on the plateau to commence. We show that, if proto-inflation is power-law, it does not suffer from a sub-Planckian eternal inflationary stage, which would otherwise be a problem. A simple model realisation is constructed in the context of α-attractors, which can both generate the inflationary plateau and the exponential slopes around it, necessary for the two inflation stages. Our mechanism allows to assume chaotic initial conditions at the Planck scale for proto-inflation, it is generic and it is shown to work without fine-tuning
More on Emergent Dark Energy from Unparticles
In a recent paper \cite{Artymowski:2020zwy} we suggested the possibility that
the present acceleration of the Universe is due to thermodynamical behavior of
unparticles. The model is free of scalar fields, modified gravity, a
Cosmological Constant (CC), the coincidence problem, initial conditions problem
and possesses interesting distinct predictions regarding the equation of state
of Dark Energy, the growth rate and the number of relativistic degrees of
freedom at BBN and CMB decoupling. In this work, we relate to a recent paper
\cite{Abchouyeh:2021wey}, which discusses a similar setup of unparticles with
and without a CC as an external source of late-time acceleration. The authors
have shown how such a model is inconsistent with the data. We show that these
claims are viable only in a particular part of the parameter space and that
model \cite{Artymowski:2020zwy} stands tall. We further suggest a consistency
condition in terms of observables. We then fit publicly available supernovae
data to derive the expected Hubble parameter and constrain the parameters of
the model.Comment: 9 pages, 9 figure
Classical bouncing Universes from vector fields
For the anisotropic Universe filled with massless vector field in the General
Relativity frame we obtain bouncing solution for one of scale factors. We
obtain the Universe with finite maximal energy density, finite value of
and
non-zero value of a scale factor for directions transverse to a vector field.
Such a bounce can be also obtained for a massive vector field with kinetic
initial conditions, which gives isotropic low energy limit. We discuss the
existence of a bounce for a massless vector field with additional matter
fields, such as cosmological constant or dust. We also discuss bouncing
solution for massless vector field domination in dimensional space-time.Comment: 11 pages, 2 figures, plain LaTe
Observational hints on the Big Bounce
In this paper we study possible observational consequences of the bouncing
cosmology. We consider a model where a phase of inflation is preceded by a
cosmic bounce. While we consider in this paper only that the bounce is due to
loop quantum gravity, most of the results presented here can be applied for
different bouncing cosmologies. We concentrate on the scenario where the scalar
field, as the result of contraction of the universe, is driven from the bottom
of the potential well. The field is amplified, and finally the phase of the
standard slow-roll inflation is realized. Such an evolution modifies the
standard inflationary spectrum of perturbations by the additional oscillations
and damping on the large scales. We extract the parameters of the model from
the observations of the cosmic microwave background radiation. In particular,
the value of inflaton mass is equal to GeV. In
our considerations we base on the seven years of observations made by the WMAP
satellite. We propose the new observational consistency check for the phase of
slow-roll inflation. We investigate the conditions which have to be fulfilled
to make the observations of the Big Bounce effects possible. We translate them
to the requirements on the parameters of the model and then put the
observational constraints on the model. Based on assumption usually made in
loop quantum cosmology, the Barbero-Immirzi parameter was shown to be
constrained by from the cosmological observations. We have
compared the Big Bounce model with the standard Big Bang scenario and showed
that the present observational data is not informative enough to distinguish
these models.Comment: 25 pages, 8 figures, JHEP3.cl
Loop Quantum Cosmology corrections to inflationary models
In the recent years the quantization methods of Loop Quantum Gravity have
been successfully applied to the homogeneous and isotropic
Friedmann-Robertson-Walker space-times. The resulting theory, called Loop
Quantum Cosmology (LQC), resolves the Big Bang singularity by replacing it with
the Big Bounce. We argue that LQC generates also certain corrections to field
theoretical inflationary scenarios. These corrections imply that in the LQC the
effective sonic horizon becomes infinite at some point after the bounce and
that the scale of the inflationary potential implied by the COBE normalisation
increases. The evolution of scalar fields immediately after the Bounce becomes
modified in an interesting way. We point out that one can use COBE
normalisation to establish an upper bound on the quantum of length of LQG.Comment: 16 pages, 1 figure, plain Late
Inflation from non-minimally coupled scalar field in loop quantum cosmology
The FRW model with non-minimally coupled massive scalar field has been
investigated in LQC framework. Considered form of the potential and coupling
allows applications to Higgs driven inflation. Out of two frames used in the
literature to describe such systems: Jordan and Einstein frame, the latter one
is applied. Specifically, we explore the idea of the Einstein frame being the
natural 'environment' for quantization and the Jordan picture having an
emergent nature. The resulting dynamics qualitatively modifies the standard
bounce paradigm in LQC in two ways: (i) the bounce point is no longer marked by
critical matter energy density, (ii) the Planck scale physics features the
'mexican hat' trajectory with two consecutive bounces and rapid expansion and
recollapse between them. Furthermore, for physically viable coupling strength
and initial data the subsequent inflation exceeds 60 e-foldings.Comment: Clarity improved. Replaced with revised version accepted in JCA