The astrophysical consequences of the presence of a quintessence scalar field on the evolution of the horizon and on the accretion disk surrounding a static black hole, in the scalar–vector–tensor version of modified gravity (MOG), are investigated. The positions of the stable circular orbits of the massive test particles, moving around the central object, are obtained from the extremum of the effective potential. Detailed calculations are also presented to investigate the light deflection, shadow and Shapiro effect for such a black hole. The electromagnetic properties of the accretion disks that form around such black holes are considered in detail. The energy flux and efficiency parameter are estimated analytically and numerically. A comparison with the disk properties in Schwarzschild geometry is also performed. The quantum properties of the black hole are also considered, and the Hawking temperature and the mass loss rate due to the Hawking radiation are considered. The obtained results may lead to the possibility of direct astrophysical tests of black hole type objects in modified gravity theories.

South Africa

Iran

Canada

Haidar Sheikhahmadi

Saheb Soroushfar

S. Sajadi

Romania

Tiberiu Harko

Astrophysical and electromagnetic emissivity properties of black holes surrounded by a quintessence type exotic fluid in the scalar–vector–tensor modified gravity

We consider a warm inflationary scenario in which the two major fluid components of the early Universe, the scalar field and the radiation fluid, evolve with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is a combination of the two fluid four-velocities. Due to the presence of anisotropies the overall cosmological evolution is also anisotropic. We obtain the gravitational field equations of the non-comoving scalar field–radiation mixture for a Bianchi Type I geometry. By assuming the decay of the scalar field, accompanied by a corresponding radiation generation, we formulate the basic equations of the warm inflationary model in the presence of two non-comoving components. By adopting the slow-roll approximation the theoretical predictions of the warm inflationary scenario with non-comoving scalar field and radiation fluid are compared in detail with the observational data obtained by the Planck satellite in both weak dissipation and strong dissipation limits, and constraints on the free parameters of the model are obtained. The functional forms of the scalar field potentials compatible with the non-comoving nature of warm inflation are also obtained.

China

Warm inflation with non-comoving scalar field and radiation fluid

In this paper, we analyze the inflationary cosmology using string field theory. This is done by using the zero level contribution from string field theory, which is a non-local tachyonic action. We will use the non-local Friedmann equations for this model based on string field theory, and calculate the slow-roll parameters for this model. We will then explicitly obtain the scalar and tensorial power spectrum, their related indices, and the tensor-to-scalar ratio for this model. Finally, we use cosmological data from Planck 2013 to 2018 to constrain the free parameters in this model, and find that string field theory is compatible with them.

Mir Faizal

Ali Aghamohammadi

Russia

Estonia

Sebastian Bahamonde

Inflation in string field theory

We investigate warm inflationary scenario in which the accelerated expansion of the early Universe is driven by chameleon-like scalar fields. Due to the non-minimal coupling between the scalar field and the matter sector, the energy-momentum tensor of each fluid component is not conserved anymore, and the generalized balance equation is obtained. The new source term in the energy equation can be used to model warm inflation. On the other hand, if the coupling function varies slowly, the model reduces to the standard model used for the description of cold inflation. To test the validity of the warm chameleon inflation model, the results for warm inflationary scenarios are compared with the observational Planck2018 Cosmic Microwave Background data. In this regard, the perturbation parameters such as the amplitude of scalar perturbations, the scalar spectral index and the tensor-to-scalar ratio are derived at the horizon crossing in two approximations, corresponding to the weak and strong dissipative regimes. As a general result it turns out that the theoretical predictions of the chameleon warm inflationary scenario are consistent with the Planck 2018 observations.

Italy

Abolhassan Mohammadi

Chile

Ramón Herrera

India

Christian Corda

Amare Abebe

Khaled Saaidi

Constraining chameleon field driven warm inflation with Planck 2018 data

We study an extension of quasi-single field model of inflation containing multiple semi-heavy isocurvaton fields using the Schwinger–Keldysh mechanism. We calculate the amplitudes and the shapes of the bispectrum and the trispectrum. We show that the diagrammatic approach associated with the Schwinger–Keldysh mechanism simplifies the analysis considerably compared to standard in-in formalism. This method is helpful to study the spectroscopy of masses and couplings of light and semi-heavy fields during inflation.

Schwinger–Keldysh mechanism in extended quasi-single field inflation

During this work, using subtraction renormalization mechanism, zero point quantum fluctuations for bosonic scalar fields in a de-Sitter like background are investigated. By virtue of the observed value for spectral index, <math id="M1"><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>(</mo><mi>k</mi><mo>)</mo></math>, for massive scalar field the best value for the first slow roll parameter, <math id="M2"><mrow><mi>ϵ</mi></mrow></math>, is achieved. In addition, the energy density of vacuum quantum fluctuations for massless scalar field is obtained. The effects of these fluctuations on other components of the universe are studied. By solving the conservation equation, for some different examples, the energy density for different components of the universe is obtained. In the case which all components of the universe are in an interaction, the different dissipation functions, <math id="M3"><mrow><msub><mrow><mover><mrow><mi>Q</mi></mrow><mo>~</mo></mover></mrow><mrow><mi>i</mi></mrow></msub></mrow></math>, are considered. The time evolution of <math id="M4"><msub><mrow><mi>ρ</mi></mrow><mrow><mi>D</mi><mi>E</mi></mrow></msub><mo>(</mo><mi>z</mi><mo>)</mo><mo>/</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mi>c</mi><mi>r</mi><mi>i</mi></mrow></msub><mo>(</mo><mi>z</mi><mo>)</mo></math> shows that <math id="M5"><mover><mrow><mi>Q</mi></mrow><mo>~</mo></mover><mo>=</mo><mn>3</mn><mi>γ</mi><mi>H</mi><mo>(</mo><mi>t</mi><mo>)</mo><msub><mrow><mi>ρ</mi></mrow><mrow><mi>m</mi></mrow></msub></math> has the best agreement in comparison to observational data including CMB, BAO, and SNeIa data set.

The Effect of de-Sitter Like Background on Increasing the Zero Point Budget of Dark Energy

In this work, an interacting chameleon-like scalar field scenario, by considering SNeIa, CMB, BAO, and OHD data sets, is investigated. In fact, the investigation is realized by introducing an ansatz for the effective dark energy equation of state, which mimics the behavior of chameleon-like models. Based on this assumption, some cosmological parameters, including the Hubble, deceleration, and coincidence parameters, in such a mechanism are analyzed. It is realized that, to estimate the free parameters of a theoretical model, by regarding the systematic errors it is better that the whole of the above observational data sets would be considered. In fact, if one considers SNeIa, CMB, and BAO, but disregards OHD, it maybe leads to different results. Also, to get a better overlap between the contours with the constraint χm2≤1 , the χT2 function could be re-weighted. The relative probability functions are plotted for marginalized likelihood L(Ωm0,ω1,β) according to the two dimensional confidence levels 68.3, 90, and 95.4% . Meanwhile, the value of the free parameters which maximize the marginalized likelihoods using the above confidence levels are obtained. In addition, based on these calculations the minimum value of χ2 based on the free parameters of the ansatz for the effective dark energy equation of state is achieved.

Sayed Wrya Rabiei

Interacting scalar tensor cosmology in light of SNeIa, CMB, BAO and OHD observational data sets

In this work, the effects of non-commutative and commutative vacua on the phase space generated by a scalar field in a scalar torsion scenario are investigated. For both classical and quantum regimes, the commutative and non-commutative cases are compared. To take account the effects of non-commutativity, two well known non-commutative parameters, θ and β , are introduced. It should be emphasized, the effects of β which is related to momentum sector has more key role in comparison to θ which is related to space sector. Also the different boundary conditions and mathematical interpretations of non-commutativity are explored.