The bouncing universe provides a possible solution to the Big Bang singularity problem. In this paper we study the bouncing solution in the universe dominated by the Quintom matter with an equation of state (EoS) crossing the cosmological constant boundary. We will show explicitly the analytical and numerical bouncing solutions in three types of models for the Quintom matter with an phenomenological EoS, the two scalar fields and a scalar field with a modified Born-Infeld action. *

We study in this paper the perturbations of the quintom dark energy model and the effects of quintom perturbations on the current observations. Quintom describes a scenario of dark energy where the equation of state gets across the cosmological constant boundary w = −1 during evolution. We present a new method to show that the conventional dark energy models based on single k-essence field and perfect fluid cannot act as quintom due to the singularities and classical instabilities of perturbations around w = −1. One needs to add extra degrees of freedom for successful quintom model buildings. There are no singularities or classical instabilities in perturbations of realistic quintom models and they are potentially distinguishable from the cosmological constant. Basing on the realistic quintom models in this paper we provide one way to include the perturbations for dark energy models with parametrized equation of state across −1. Compare with those assuming no dark energy perturbations, we find that the parameter space which allows the equation of state to get across −1 will be enlarged in general when including the perturbations.

Current observations seem to mildly favor an evolving dark energy with the equation of state getting across -1. This form of dark energy, dubbed Quintom, is studied phenomenologically in this paper with an oscillating equation of state. We find oscillating Quintom can unify the early inflation and current acceleration of the universe, leading to the oscillations of the Hubble constant and a recurring universe. Our oscillating Quintom would not lead to a big crunch nor big rip. The scale factor keeps increasing from one period to another and leads naturally to a highly flat universe. The universe in this model recurs itself and we are only staying among one of the epochs, in which sense the coincidence problem is reconciled. PACS numbers: 98.80.Cq In 1998, two groups [1, 2] independently showed the accelerating expansion of our universe, which established the existence of dark energy where the equation of state is less than −1/3 today. The simplest form of dark energy is the cosmological constant. A cosmological constant which leads to current acceleration would encounter many theoretical problems, such as the fine-tuning problem and the coincidence problem [3]. A light scalar field of quintessence [4,5,6] which evolves with time is to some extent likely to resolve the coincidence problem. The model of phantom [7] has also been put forward which leads to an equation of state w ≤ −1. Normally quintessence with a canonic kinetic term can only have w ≥ −1, meanwhile k-essence[8] can have both w ≥ −1 and w < −1. For the cosmological constant and many quintessence models the event horizon would lead to a potential incompatibility with the string theory, meanwhile for models where w < −1 one would get the Big Rip[9] of the universe.The accumulation of the current observational data has opened a robust window for probing the recent behavior of dark energy. Measurements from type Ia Supernova (SNe Ia), the Cosmic Microwave Background (CMB) Radiation, Large Scale Structure (LSS), weak lensing, clusters and galaxies all contain the imprints of dark energy. Specifically the recently released first year Wilkinson Microwave Anisotropy Probe (WMAP) measurement[10], the Sloan Digital Sky Survey (SDSS) measurement of the three-dimensional power spectrum [11] and most importantly, the recent discovery of 16 SNe Ia [12] with the Hubble Space Telescope during the GOODS ACS Treasury survey, together with former SNe Ia data have provided the most precise up-to-date measurements of dark energy. Many other sources have also been studied to make crosschecks and reveal new physics on the dark energy and the concordance cosmological model. Recently many authors in the literature have fitted the behavior of dark energy using various parameterizations. The best fit value of the equation of state is found to be less than −1 when using SNe Ia [12,13,14,15,16,17] or the X-ray mass fraction data[18] with a cosmological constant still well within the central regions 1 . It has also been pointed out by many authors that an evolving dark energy ...

We present nonsingular, homogeneous and isotropic bouncing solutions of the conformal Galileon model. We show that such solutions necessarily begin with a radiation-dominated contracting phase. This is followed by a quintom scenario in which the background equation of state crosses the cosmological constant boundary allowing for a nonsingular bounce which in turn is followed by Galilean Genesis. We analyze the spectrum of cosmological perturbations in this background. Our results show that the fluctuations evolve smoothly and without any pathology, but the adiabatic modes form a blue tilted spectrum. In order to achieve a scale-invariant primordial power spectrum as required by current observations, we introduce a light scalar field coupling to the Galileon kinetically. We find two couplings which yield a scale-invariant spectrum, one of which requires a fine tuning of the initial conditions. This model also predicts a blue tilted spectrum of gravitational waves stemming from quantum vacuum fluctuations in the contracting phase.

Ethylene is a gaseous phytohormone that plays vital roles in plant growth and development. Previous studies uncovered EIN2 as an essential signal transducer linking ethylene perception on ER to transcriptional regulation in the nucleus through a "cleave and shuttle" model. In this study, we report another mechanism of EIN2-mediated ethylene signaling, whereby EIN2 imposes the translational repression of EBF1 and EBF2 mRNA. We find that the EBF1/2 3' UTRs mediate EIN2-directed translational repression and identify multiple poly-uridylates (PolyU) motifs as functional cis elements of 3' UTRs. Furthermore, we demonstrate that ethylene induces EIN2 to associate with 3' UTRs and target EBF1/2 mRNA to cytoplasmic processing-body (P-body) through interacting with multiple P-body factors, including EIN5 and PABs. Our study illustrates translational regulation as a key step in ethylene signaling and presents mRNA 3' UTR functioning as a "signal transducer" to sense and relay cellular signaling in plants. VIDEO ABSTRACT.

Dark-grown Arabidopsis seedlings develop an apical hook when germinating in soil, which protects the cotyledons and apical meristematic tissues when protruding through the soil. Several hormones are reported to distinctly modulate this process. Previous studies have shown that ethylene and gibberellins (GAs) coordinately regulate the hook development, although the underlying molecular mechanism is largely unknown. Here we showed that GA 3 enhanced while paclobutrazol repressed ethylene-and EIN3-overexpression (EIN3ox)-induced hook curvature, and della mutant exhibited exaggerated hook curvature, which required an intact ethylene signaling pathway. Genetic study revealed that GA-enhanced hook development was dependent on HOOKLESS 1 (HLS1), a central regulator mediating the input of the multiple signaling pathways during apical hook development. We further found that GA 3 induced (and DELLA proteins repressed) HLS1 expression in an ETHYLENE INSENSITIVE 3/EIN3-LIKE 1 (EIN3/ EIL1)-dependent manner, whereby EIN3/EIL1 activated HLS1 transcription by directly binding to its promoter. Additionally, DELLA proteins were found to interact with the DNA-binding domains of EIN3/EIL1 and repress EIN3/EIL1-regulated HLS1 expression. Treatment with naphthylphthalamic acid, a polar auxin transport inhibitor, repressed the constitutively exaggerated hook curvature of EIN3ox line and della mutant, supporting that auxin functions downstream of the ethylene and GA pathways in hook development. Taken together, our results identify EIN3/EIL1 as a new class of DELLA-associated transcription factors and demonstrate that GA promotes apical hook formation in cooperation with ethylene partly by inducing the expression of HLS1 via derepression of EIN3/EIL1 functions.

We search for signatures of Lorentz and violations in the cosmic microwave background (CMB) temperature and polarization anisotropies by using the Wilkinson Microwave Anisotropy Probe (WMAP) and the 2003 flight of BOOMERANG (B03) data. We note that if the Lorentz and symmetries are broken by a Chern-Simons term in the effective Lagrangian, which couples the dual electromagnetic field strength tensor to an external four-vector, the polarization vectors of propagating CMB photons will get rotated. Using the WMAP data alone, one could put an interesting constraint on the size of such a term. Combined with the B03 data, we found that a nonzero rotation angle of the photons is mildly favored: [Formula: See Text].

We propose in this paper a scenario of spontaneous baryogenesis in cosmological models of Quintessence by introducing a derivative coupling of the Quintessence scalar Q to the baryon current J µ B or the current of the baryon number minus lepton number J µ B−L . We find that with a dimension-5 operator ∂µQJ µ B−L suppressed by the Planck mass M pl or the Grand Unification Scale MGUT , baryon number asymmetry nB/s ∼ 10 −10 can be naturally explained via leptogenesis. We study also the isocurvature baryon number fluctuation generated in our model. PACS numbers: 98.80.CqEvidence is increasing that Universe is spatially flat and accelerating at present time [1]. The simplest account of the cosmic acceleration seems to be a remnant small cosmological constant Λ, however many physicists are attracted by the idea that a new form of matter is causing the cosmic acceleration. This new form of matter is not clustered gravitationally on the scale of the galaxy clusters and has been usually called dark energy or Quintessence [2-5].For Quintessence, typically one assumes the existence of a scalar field Q (or multi scalar fields) which is taken to be homogeneous in space and via its kinetic and potential energy contributions to the energy-momentum tensor tuned to provide an equation of state leading to accelerated expansion, beginning to dominate the matter content of the Universe today. Models of Quintessence can have interesting cosmological properties including tracking behavior.Generally minimal or non-minimal couplings of Quintessence with gravitation are considered in the literature [6]. Being a dynamical field, Quintessence is expected to have interactions with the ordinary matters [7], however as argued in Refs.[8] for most of cases the couplings are strongly constrained. But there are exceptions. For example, Carroll [8] has considered an interaction of form QF µνF µν with F µν being the electromagnetic field strength tensor and studied its implication on the rotation of the plane of polarization of light coming from distant sources. In this paper we introduce a type of interaction of Quintessence with the matter, which in terms of an effective lagrangian is given bywhere M is the cut-off scale which for example could be the Planck mass M pl or the scale of Grand Unification Theory M GUT , and c is the coupling constant which characterizes the strength of Quintessence interacting with the ordinary matter in the Standard Model of the electroweak theory. Specifically we take in this paper J µ to be the baryon current J µ B or the current of baryon number minus lepton number J µ B−L , and study their implications on baryogenesis. The lagrangian in Eq.(1) involves derivative and obeys the symmetry Q → Q + constant [8], so the Quintessence potential will not be modified by the quantum corrections.The mechanism of generating the baryon number asymmetry in this paper follows closely the spontaneous baryogenesis [9,10]. The term in Eq.(1), whenQ is non-zero during the evolution of spatial flat Friedmann-Robertson-Walker Univ...