Research
Interacting dark energy model
Dark energy and dark matter are two major scientific issues in fundamental physics in the 21st century. Except for gravitational interaction, the direct non-gravitational interaction that does not violate current observational constraints should also be taken into consideration. Dark energy is usually considered as a non-adiabatic fluid, which may cause the early time large-scale instability. In order to solve this problem, the PPF framework was put forward to calculate the cosmological perturbations. Under this framework, there is no need to calculate the density and velocity perturbations, which can avoid the instability successfully. We propose a simple parameterization steering clear of this problem, which is more general and can be applied to explore the interaction between dark matter and dark energy by various cosmological data.
References
Ma, C. P., & Bertschinger, E. 1995, ApJ, 455, 7 (perturrbation theory)
Väliviita, J., Majerotto, E., & Maartens, R. 2008, JCAP, 07, 020 (large scale instability)
Hu, W. 2008, PhRvD, 77, 103524 (PPF framework)
Li, Y. H., Zhang, J. F., & Zhang, X. 2014, PhRvD, 90, 063005 (PPF frame work for IDE model)
My work
Dai, J. P., & Xia, J. Q. 2019, APJ, 876, 125
Non-Gaussianity
The standard inflationary paradigm predicts a flat Universe perturbed by nearly Gaussian and scale invariant primordial perturbations. These predictions have been confirmed by the increasingly precise measurements of the CMB and the large-scale structure (LSS). Since the last decade, the Planck satellite has confirmed that the initial seeds of structure must have been close to Gaussianity. However, it is difficult to discriminate between the vast array of inflationary scenarios since most of the present constraints on the Lagrangian of the inflaton field have been obtained from measurements of the two-point function, or power spectrum. Therefore, it is natural to study the non-Gaussianity signatures in higher order correlators.
My interest is using LSS power spectrum and bispectrum to constrain the local type primordial non-Gaussianity and its running.
References
Bernardeau, F., Colombi, S., Gaztanaga, E., & Scoccimarro, R. 2002, Physics reports, 367(1-3), 1-248. (A very nice review about cosmological pertubation theory)
Liguori, M., Sefusatti, E., Fergusson, J. R., & Shellard, E. P. S. 2010, Advances in Astronomy, 2010. (A review about primordial non-Gaussianity and bispectrum measurements)
Xia J.-Q., Viel M., Baccigalupi C., De Zotti G., Matarrese S., Verde L., 2010, The Astrophysical Journal Letters, 717, L17 (Using power spectrum to constrain non-Gaussianity)
My work
Dai, J. P., & Xia, J. Q. 2020, MNRAS Letters, 491, L61
Skew Spectrum
Clustering of the large scale structure provides complementary information to the measurements of the cosmic microwave background anisotropies through power spectrum and bispectrum of density perturbations. Extracting the bispectrum information, however, is more challenging than it is from the power spectrum due to the complex models and the computational cost to measure the signal and its covariance. To overcome these problems, we adopt a proxy statistic, skew spectrum which is a cross-spectrum of the density field and its quadratic field. By applying a large smoothing filter to the density field, we show the theory fits the simulations very well. With the spectra and their full covariance estimated from N-body simulations as our “mock” Universe, we perform a global fits for the cosmological parameters. The results show that adding skew spectrum to power spectrum the 1σ marginalized errors for cosmological parameters are reduced by 20-40 %. This is the answer to the question posed in the title and indicates that the skew spectrum will be a fast and effective method to access complementary information to that enclosed in the power spectrum measurements, especially for the forthcoming generation of wide-field galaxy surveys.
My work
1. Halo skew spectrum + RSD: Dai, J. P., Licia, V., & Xia, J. Q. 2020, JCAP, 202008, 007
2. Multi-tracer: Dai, J. P., & Xia, J. Q. 2020, APJ, 905, 127
3. apply to data
Fast Radio Bursts
Recently, since the first detection of fast radio burst, it has been a hotspot in astrophysics. FRBs are millisecond radio transients at GHz frequencies characterized by the excess dispersion measure with respect to the Galactic values. The localization of the repeating sources FRB 121102 and FRB 180924 provides us a good reason to believe FRBs originate from cosmological distance. So it is very interesting to investigate the potential of FRBs in cosmology.
My interest is using the large-scale clustering statistics of dispersion measures of FRBs to study the cosmology problems. The advantage of this method is that we only need the normalized redshift distributions of FRBs catalog, instead of the precise redshift information for each FRB.
My work
1. Baryon Fraction in Intergalactic Medium: Dai, J. P. & Xia, J. Q. 2021, MNRAS, 503, 4576
2. Reionization: Dai, J. P. & Xia, J. Q. 2021, JCAP, 202105, 050