Dark energy through derivatives of matter fields

Shahab Shahidi

School of Physics, Damghan University

Abstract: In this talk, I will try to explore the possibility of extracting dark energy effects from derivatives of the baryonic matter Lagrangian. I will give some motivations about the idea and then build a gravitational theory containing these derivatives. I will then investigate the background and also first order cosmological perturbations of the theory. I will find the best fit values for the model parameter using observations on the Hubble parameter and also f\sigma_8 data. We will see that the cosmological observations could be satisfied in this model, but we should care more about the accelerating phase of the universe. At last, I will give some comments about the problems and also possible solutions.

یکشنبه 20 مهر 1399، ساعت  15:00

Sunday 11 October 2020 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

**لطفا  به  ساعت سمینار توجه فرمایید**

The Radio-IR correlation in Galaxies: Origins and Applications

Fatemeh Tabatabaei

School of Astronomy, Institute of Research in Fundamental Sciences (IPM)

Abstract: The tight empirical correlation between infrared (IR) and radio continuum luminosities in star-forming galaxies that was discovered following the IRAS mission has attracted a lot of interest among both theorists and observers. Our understanding of the physics underpinning this correlation is however still largely incomplete and in need of a satisfactory explanation. The correlation has conventionally been explained by the idea that the IR and radio emission are both being driven by the energy input from massive stars, and thus star formation. However, this connection is complicated by the observation that the IR emission consists of at least two components; one heated directly by massive stars and one heated by the diffuse interstellar radiation field which includes emission from the old stellar population. Similarly, the connection between nonthermal radio emission and massive stars is complicated by the advection and diffusion of cosmic ray electrons from their place of birth and by the magnetic fields that regulate the synchrotron emission in the interstellar medium.
Theoretical studies suggest that several factors could conspire to keep the correlation linear. This conspiracy is particularly indicated in the low-mass, low metallicity galaxies, which are expected to be radio-dim for the same level of star formation as in larger galaxies, but again they follow the empirical radio-IR relation. Our lack of understanding of the underlying physics of the radio-IR correlation becomes obvious at high redshift where theoretical models predict a deficit of radio emission leading to clear deviations from the local radio-IR correlation. However, no compelling evidence of such a deviation has been observed out to z~3. Resolved studies should help in understanding the physics of the radio-IR correlation and provide a test bed for existing models. Is the correlation indeed a gift from Nature, allowing us to study star formation throughout the universe by exploiting the high angular resolution and sensitivity of modern radio interferometers and IR detectors? Thanks to satellites operating in the mid- and far-IR such as Spitzer and Herschel, along with modern radio telescopes such as the JVLA, LOFAR and others, several studies have been performed in recent years focusing on both the integrated and spatially-resolved radio-IR correlation, vastly increasing our understanding of this crucial relation.

یکشنبه 6 مهر 1399، ساعت 15:00

Sunday 27 September 2020 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Observational Measures of Halo Properties Beyond Mass

Peter Behroozi

Department of Astronomy and Steward Observatory, University of Arizona

Abstract: Different properties of dark matter haloes, including growth rate, concentration, interaction history, and spin, correlate with environment in unique, scale-dependent ways.  While these halo properties are not directly observable, galaxies will inherit their host haloes’ correlations with environment.  As a result, measures of environment have the potential to reveal how galaxy properties are correlated with halo properties beyond halo mass.  We show preliminary results that different halo properties imprint distinct scale-dependent signatures in both the two-point correlation function and the distribution of distances to kth nearest neighbors.  We show that these signatures are strong, and are accessible even with low-resolution (e.g., grism) spectroscopy at higher redshifts.  Comparing observed two-point correlation functions for large and small galaxies at z=0, we use these results to show that classic galaxy size models (i.e., galaxy size being proportional to halo spin) cannot be correct.  Instead, we find that models where galaxy size depends inversely on concentration are a better match to observations.

یکشنبه 30 شهریور 1399، ساعت 19:00

Sunday 20 September 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Cosmological parameters from cosmic dynamics: new methods based on voids and flows

Guilhem Lavaux

Institut d’Astrophysique de Paris (IAP)

Abstract: Cosmology is in a golden age. The present paradigms are sufficiently firm to derive a large number of results on the universe, the data is becoming abundant and we have computers to analyze them. However some clouds are gathering at the horizon. There is an increase in tension on the Hubble constant, the properties of the hypothetical dark energy are still largely unconstrained and we will soon face an over-abundance of data which will reduce statistical errors to a negligible amount. Standard analyses have been relying a lot on statistics of the 2-point correlation function, which is not capable of handling well systematic effects. As such, we should look at other old and new probes of cosmology. I will discuss two probes of the dynamics to which I contributed significantly: the use cosmic voids to probe expansion, and the reconstruction of cosmic velocities to constrain the strength of gravity. We will see how the ideas have grown, and expanded recently and some new promising results concerning the reconstruction aspects.

دوشنبه 24 شهریور 1399، ساعت 19:00

Monday 14 September 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Testing MOG theory and CDM model at galactic and cosmic scales using observational data

Zahra Davari

Physics Department Sharif University of Technology

Abstract: In this talk, I will discuss one of the alternative theories to dark matter named MOdified Gravity (MOG) on both the galactic and cosmic scales.

 In the first part, I have investigated MOG theory and dark matter model by testing their ability to describe the local dynamics of the Milky Way in vertical and transverse directions by using observation data such as the vertical dispersion, rotation curve, surface density, and number density of stars.
The results show that two models of MOG and CDM are able to describe equally well the rotation curve and the vertical dynamics of stars in the local MW.
In the second part, I characterize the main aspects of the MOG theory at cosmological scales, analyzing the Friedmann equations and the expressions of the scalar fields of the theory. I use data from the binned Pantheon SNIa dataset,  Cosmic Chronometers (CC), and Big Bang Nucleosynthesis to test MOG predictions and comparing to the LCDM model.

یکشنبه 16 شهریور 1399، ساعت 19:00

Sunday 6 September 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Causal Set Theory and Cosmology

Yasaman Yazdi

Theoretical Physics Group, Blackett Laboratory, Imperial College London

Abstract: Causal sets are fundamentally discrete structures proposed to underlie spacetime. A causal set is made of ‘atoms’ of spacetime related according to the causal relations between them. Causal structure, discreteness, covariance, and nonlocality play a prominent role in the physics described by causal sets, including cosmology. Causal set theory has touched on a number of fundamental cosmological questions. These range from the cosmological constant problem to the origin of cosmological horizon entropy. In this talk I will review some of these studies and highlight how the unique features of causal sets come into play.

یکشنبه 2 شهریور 1399، ساعت 19:00

Sunday 23 August 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

The Cosmological principle and the frame that never was

Mohamed Rameez

Niels Bohr Institute, University of Copenhagen

Abstract: The largest anisotropic feature of the Cosmic Microwave Background is the dipole, believed to originate from the relative motion of the heliocentric frame with a velocity of ~369 km/s with respect to the ‘rest frame of the Universe’ in standard cosmology. This should cause a dipolar modulation in the number counts of distant sources, through special relativistic aberration and Doppler boosting effects. We test this with various all-sky catalogues: NVSS and SUMSS radio galaxies, WISE galaxies and AGNs as well as GAIA-unWISE AGNs and consistently find a significantly larger dipole than expected, implying velocities > 1000 km/s at conservative statistical significances as high as 3.3 sigma. These and other observations hint at a bulk flow of matter in the local Universe, extending out to scales larger than is typical in \Lambda CDM N-body simulations. Convergence to the CMB rest frame has never been demonstrated. An observational effect of such a bulk flow would be a scale dependent dipolar modulation in the deceleration parameter. We look for this in the SDSS-II/SNLS-III Joint lightcurve analysis compilation of SN1a data and find such a modulation at ~3.9 sigma statistical significance, while the evidence for any isotropic acceleration of the Universe simultaneously drops to <1.4 sigma. These observations suggest that dark energy is an artefact of our idealized cosmological model.

یکشنبه 26 مرداد 1399، ساعت 19:00

Sunday 16 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Loop quantum gravity and black hole interior

سعید راستگو

Saeed Rastgoo

Department of Physics and Astronomy, University of York

Abstract: Loop Quantum Gravity (LQG) is one of the few main top-down approaches to the quantization of spacetime that originated from the gravitation community.  It has various predictions regarding quantum cosmology and quantum black holes. This talk is divided into two parts. In the first part I will briefly explain what  LQG is all about and what are its main general predictions. In the second part, I will concentrate on black holes and sketch how this theory quantizes the interior of the Schwarzschild black hole and predicts the resolution of its classical singularity and a bounce to a white hole.

یکشنبه 19 مرداد 1399، ساعت 19:00

Sunday 9 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Late time universe as a probe of cosmic origins

آزاده مرادی نژاد دیزگاه

Azadeh Moradinezhad Dizgah

Department of theoretical physics, University of Geneva

**لطفا  به ساعت نامتعارف سمینار توجه فرمایید** 

Abstract: The non-Gaussianity of the initial conditions leaves its imprints on the large scale structure. While the upcoming galaxy surveys will provide data with an unprecedented volume and precision, a novel observational technique referred to as line intensity mapping is also attracting significant amount of attention, given its unique potential to probe the universe at the range of scales and redshifts not accessible to galaxy surveys. In this talk, I will discuss a few different aspects of using these two observational windows to constrain primordial non-Gaussianity. In particular, I’ll discuss (a) the prospects of intensity mapping with CO and [CII] emission lines and its synergies with galaxy surveys, (b) the impact of modes larger than the size of a given survey on the measurement of clustering statistics within the survey, (c) the optimal estimators to extract information from clustering bispectrum.

یکشنبه 12 مرداد 1399، ساعت 19:00

Sunday 2 August, 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vclass.ecourse.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest