On a dark energy model explicitly parametrised by the deceleration parameter

Transcription

1 On a dark energy model explicitly parametrised by the deceleration parameter Martiros Khurshudyan University of Science and Technology of China

2 On a dark energy model explicitly parametrised by the deceleration parameter Short introduction known facts Gaussian Processes (with H(z) data) some applications Our Dark Energy model and GP Some results Conclusion

3 Short introduction known facts Large scale universe Dark energy has enough negative pressure to work against gravity. Dark matter is going to be something having attractive nature. Models of dark energy cosmological constant(the first dark energy model), varying cosmological constant models, quintessence, phantom, k-essence (scalar field representations), ghost dark energy, holographic dark energy (the energy density is parametrised), Chaplygin gas (dark energy and dark matter joint model with a non-linear EoS) Alternative approach a modification of gravity (I will skip the discussion on this issue because the community is very well familiar with this idea)

4 Gaussian processes (with H(z) data) The Gaussian distribution presents a distribution of a random variable characterized by a mean and a covariance. GP should be understood as a distribution over functions, characterized by a mean function and a covariance matrix. The covariance function (kernel) which correlates the function H(z) at different points We use GaPP code by Marina Seikel et al... Marina Seikel, Chris Clarkson, Mathew Smith, JCAP 06 (2012), 036 Ming-Jian Zhang, Jun-Qing Xia, JCAP 1612 (2016) no.12, 005

5 Gaussian processes

6 Gaussian processes

7 Gaussian Processes (with H(z) data) - some applications How we can use GP with IDE? It is very simple task if EoS of DE is given How we can use GP in case of CC? eventually the interaction term Q will be expressed as a function of EoS of DE, the Hubble parameter and its higher order derivatives

8 Gaussian Processes (with H(z) data) - some applications How we can use GP in cosmology with particle creation when we have IDE? It is very simple task if EoS of DE is given and the form of the particle creation is assumed eventually the interaction term Q will be expressed as a function of EoS of DE, the Hubble parameter and its higher order derivatives and other parameters describing the particle creation rate

9 Our Dark Energy model and GP Motivation of the research The result reported by the BOSS experiment for the Hubble parameter at z = 2.34 is a direct evidence for the existence of a nongravitational coupling between dark energy and dark matter. Our dark energy model q is the deceleration parameter H(2.34) = 222 ± 7 The main results obtained from direct numerical integration H(2.34) = 222 ± 7 result can be explained without interaction and the EoS we have considered is in no way strange But this is fully model dependent result!!!!! E. Elizalde, M. Khurshudyan, S. Nojiri, IJMPD (2018) T. Delubac et al. [BOSS Collaboration], Astron. Astrophys. 574 (2015), A59 E. G. M. Ferreira, J. Quintin, A. A. Costa, E. Abdalla and B. Wang, Phys. Rev. D 95 (2017) no.4,

10 Interacting Dark Energy models and GP How we can use GP with IDE? It is very simple task if EoS of DE is given eventually the interaction term Q will be expressed as a function of EoS of DE, the Hubble parameter and its higher order derivatives

11 Conclusion from this study The main message from direct numerical integration 1. The model can explain reported value of the Hubble parameter without nongravitational interaction. 2. The EoS we have considered is in no way strange The main message from GP 1. we need in this case to involve a non-gravitational interaction between dark energy and dark matter, to explain the mentioned value of the Hubble parameter. 2. However, even if it would seem we do need to include a non-gravitational interaction, this occurs for redshifts not covered by recent H(z) data. we do not have a final answer to the main question!!!!!

12 Some results 1. The model according 68% C.L. of the reconstruction with 40 sample H(z) data can be accepted. 2. The model according 68% C.L. of the reconstruction with 30 sample H(z) data can be accepted. 3. According to that, either a or an ω -singularity (Type V) can be generated S. Nojiri, S. D. Odintsov and S. Tsujikawa, Phys. Rev. D 71 (2005) M. P. Dabrowski and T. Denkiewicz, Phys. Rev. D 79 (2009) L. Fernandez-Jambrina, Phys. Lett. B 656 (2007) 9

13 Some other results The phase space analysis with and gives

14 Conclusion We made an attempt to construct a dark energy model explicitly parametrised by the deceleration parameter. In this way we initiated a fresh direction of research concerning to dynamical dark energy models. A detailed study shows that the model (by the direct integration of the field equations) is viable and indicates that we do not need to involve non-gravitational interaction to explain the BOSS experiment result concerning to Hubble parameter at z = We performed also a model independent analysis using GP and found that in order to address the BOSS experiment issue we need data covering higher redshifts. On the other hand, we performed the phase space analysis of the models for several forms of non-gravitational interaction indicating how the cosmological coincidence problem can be solved. We have also the classification of the future finite-time singularities for suggested model.

15 Thank You for Your attention