arXiv subjects

Xiulian Wang

Publications and source records attributed to Xiulian Wang.

11 recordsLinked to original sources

arXiv2012

Metric-Affine Formalism of Higher Derivative Scalar Fields in Cosmology

Higher derivative scalar field theories have received considerable attention for the potentially explanations of the initial state of the universe or the current cosmic acceleration which they might offer. They have also attracted many interests in the phenomenological studies of infrared modifications of gravity. These theories are mostly studied by the metric variational approach in which only the metric is the fundamental field to account for the gravitation. In this paper we study the higher derivative scalar fields with the metric-affine formalism where the connections are treated arbitrarily at the beginning. Because the higher derivative scalar fields couple to the connections directly in a covariant theory these two formalisms will lead to different results. These differences are suppressed by the powers of the Planck mass and are usually expected to have small effects. But in some cases they may cause non-negligible deviations. We show by a higher derivative dark energy model that the two formalisms lead to significantly different pictures of the future universe.

gr-qc↗

arXiv2010

Spacetime variation of $α$ and the CMB power spectra after the recombination

The possible variation of the fine structure constant may be due to the non-minimal coupling of the electromagnetic field to a light scalar field which can be the candidate of dark energy. Its dynamical nature renders the fine structure constant varies with time as well as space. In this paper we point out the spatial fluctuation of the fine structure will modify the power spectra of the temperature and the polarization of the cosmic microwave background. We show explicitly that the fluctuations of the coupled scalar field generate new temperature anisotropies at the linear order and induce a $B$ mode to the polarization at higher order in general.

astro-ph.CO↗

arXiv2009

$CPT$ Violating Electrodynamics and Chern-Simons Modified Gravity

The electrodynamics with a Chern-Simons term $p_μA_ν\widetilde{F}^{μν}$ violates Lorentz and $CPT$ symmetries with a non-vanishing $p_μ$. For a fixed vector $p_μ$, in this paper we point out that the energy-momentum tensor of this theory coupled to the gravity minimally is symmetric but not divergence free, which consequently makes the gravitational field equation inconsistent. To preserve the consistency, we introduce a Chern-Simons term in the gravity sector with the coefficient determined by the Lorentz and $CPT$ violating term in the electromagnetic field. Further we study the phenomenologies of the model on the cosmic microwave background radiation and the relic gravitational waves.

hep-ph↗

arXiv2008

Testing CPT Symmetry with CMB Measurements

In this paper we study the possibility of testing \emph{CPT} symmetry with Cosmic Microwave Background (CMB) measurements. Working with an effective lagrangian of the photon with \emph{CPT} violation ${\cal L} \sim p_μA_ν\tilde F^{μν}$ which causes the polarization vectors of the propagating CMB photons rotated, we determine the rotation angle $Δα$ using the BOOMERanG 2003 and the WMAP3 angular power spectra. In this analysis we have included the newly released $TC$ and $GC$ ($l<450$) information of WMAP3 and found $Δα=-6.2\pm3.8$ deg at $1σ$ confidence level. This result increases slightly the significance for the \emph{CPT} violation obtained in our previous paper (Feng \emph{et al.}, 2006) $Δα=-6.0 \pm 4.0$ deg (1$σ$). Furthermore we examine the constraint on the rotation angle with the simulated Planck data. Our results show that the Planck will be sensitive to $Δα$ at the level of 0.057 deg and able to test the \emph{CPT} symmetry with a higher precision.

hep-ph↗

arXiv2005

Natural Inflation, Planck Scale Physics and Oscillating Primordial Spectrum

In the ``natural inflation'' model, the inflaton potential is periodic. We show that Planck scale physics may induce corrections to the inflaton potential, which is also periodic with a greater frequency. Such high frequency corrections produce oscillating features in the primordial fluctuation power spectrum, which are not entirely excluded by the current observations and may be detectable in high precision data of cosmic microwave background (CMB) anisotropy and large scale structure (LSS) observations.

astro-ph↗

arXiv2004

Dark Energy Constraints from the Cosmic Age and Supernova

Using the low limit of cosmic ages from globular cluster and the white dwarfs: $t_0 > 12$Gyr, together with recent new high redshift supernova observations from the HST/GOODS program and previous supernova data, we give a considerable estimation of the equation of state for dark energy, with uniform priors as weak as $0.2<Ω_m<0.4$ or $0.1<Ω_m h^2<0.16$. We find cosmic age limit plays a significant role in lowering the upper bound on the variation amplitude of dark energy equation of state. We propose in this paper a new scenario of dark energy dubbed Quintom, which gives rise to the equation of state larger than -1 in the past and less than -1 today, satisfying current observations. In addition we've also considered the implications of recent X-ray gas mass fraction data on dark energy, which favors a negative running of the equation of state.

astro-ph↗

arXiv2004

Reconstructing large running-index inflaton potentials

Recent fits of cosmological parameters by the first year Wilkinson Microwave Anisotropy Probe (WMAP) measurement seem to favor a primordial scalar spectrum with a large varying index from blue to red. We use the inflationary flow equations to reconstruct large running-index inflaton potentials and comment on current status on the inflationary flow. We find previous negligence of higher order slow rolling contributions when using the flow equations would lead to unprecise results.

astro-ph↗

arXiv2004

Thermal leptogenesis in a model with mass varying neutrinos

In this paper we consider the possibility of neutrino mass varying during the evolution of the Universe and study its implications on leptogenesis. Specifically, we take the minimal seesaw model of neutrino masses and introduce a coupling between the right-handed neutrinos and the dark energy scalar field, the Quintessence. In our model, the right-handed neutrino masses change as the Quintessence scalar evolves. We then examine in detail the parameter space of this model allowed by the observed baryon number asymmetry. Our results show that it is possible to lower the reheating temperature in this scenario in comparison with the case that the neutrino masses are unchanged, which helps solve the gravitino problem. Furthermore, a degenerate neutrino mass patten with $m_i$ larger than the upper limit given in the minimal leptogenesis scenario is permitted.

hep-ph↗

arXiv2003

Dark Energy and Neutrino Mass Limits from Baryogenesis

In this brief report we consider couplings of the dark energy scalar, such as Quintessence to the neutrinos and discuss its implications in studies on the neutrino mass limits from Baryogenesis. During the evolution of the dark energy scalar, the neutrino masses vary, consequently the bounds on the neutrino masses we have here differ from those obtained before.

hep-ph↗

arXiv2003

Assessing the Effects of the Uncertainty in Reheating Energy Scale on Primordial Spectrum and CMB

The details of reheating energy scale $ρ_{reh}$ is largely uncertain today, independent of inflation models. This would induce uncertainty in predicting primordial spectrum. Such uncertainty could be very large, especially for spectra with large running $n_S$. We find that for some inflation models with a large $d\ln n_S(k)/d\ln k$, $ρ_{reh}$ could be highly restricted by current CMB observations.

astro-ph↗

arXiv2001

Quintessence and Spontaneous Leptogenesis

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 $J_B^μ$ or the current of the baryon number minus lepton number $J_{B-L}^μ$. We find that with a dimension-5 operator ${\partial_μQ} J_{B-L}^μ$ suppressed by the Planck mass $M_{pl}$ or the Grand Unification Scale $M_{GUT}$, baryon number asymmetry $n_B/s \sim 10^{-10}$ can be naturally explained {\it via} leptogenesis. We study also the isocurvature baryon number fluctuation generated in our model.

hep-ph↗