Haidar Sheikhahmadi

School of Astronomy, Institute for Research in Fundamental Sciences-IPM

Self-Interacting QFT in Curved Backgrounds, the Bubble Loop Corrections

Abstract:  We consider a general Lagrangian for a massive scalar field with a conformal coupling in the dS background and study the quantum corrections from bubble loop diagrams. Employing a dimensional regularization scheme, we calculate the regularized zero-point energy density, pressure, and the trace of the energy-momentum tensor. It is shown that the classical relation of trace for the vacuum stress-energy tensor receives quantum anomaly correction which depends on the mass and the conformal coupling, while the consistency relation of zero-point energy does hold. We calculate the density contrast associated with the vacuum zero-point energy and show that perturbations are of the order of background values indicate an inhomogeneous and non-perturbative distribution of the zero-point energy. Even more, we calculate the bispectrum associated with the distribution of the zero-point energy and pressure and show that they are highly non-Gaussian. In the next step, incorporating the perturbative in-in formalism, we extend our analysis to self-interacting fields with a general potential of even orders of the field. We again calculate the quantum corrections in the vacuum zero-point energy and pressure for these fields as well. We then investigate the equation of state corresponding to these quantum corrections and examine the scaling of the divergent terms in the vacuum zero-point energy and pressure associated with the dimensional regularization scheme. We discuss some interesting aspects of free and interacting vacua and their relation as well.

یکشنبه 6 خرداد 1403، ساعت 17:00

Sunday 26 May 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3   /

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

گزینه ورود به صورت مهمان – Enter as a Guest

Raihaneh Moti

School of Astronomy, Institute for Research in Fundamental Sciences-IPM

On the GravoThermo Memory 

Abstract: In this presentation, the concepts discussed in arXiv:2307.04151 will be explored. First, I will review the gravitational memory effect. Then, the thermodynamic properties of a freely falling ensemble of gyroscopes after the passage of a weak gravitational wave will be discussed. Due to the precession memory effect, the thermodynamic quantities will experience a change because of the space-time perturbation. This GravoThermo memory effect potentially can be used for the detection of gravitational waves.

  یکشنبه 30 اردیبهشت 1403، ساعت 17:00

Sunday 19 May 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Amirmohammad Chegeni

Department of Physics and Astronomy “Galileo Galilei”, University of Padova

Clusternets: A deep learning approach to probe clustering dark energy

Abstract: Machine Learning (ML) algorithms are becoming popular in cosmology for extracting valuable information from cosmological data. In this paper, we evaluate the performance of a Convolutional Neural Network (CNN) trained on matter density snapshots to distinguish clustering Dark Energy (DE) from the cosmological constant scenario and to detect the speed of sound ($c_s$) associated with clustering DE. We compare the CNN results with those from a Random Forest (RF) algorithm trained on power spectra. Varying the dark energy equation of state parameter $w_{\rm{DE}}$ within the range of -0.7 to -0.99, while keeping $c_s^2 = 1$, we find that the CNN approach results in a significant improvement in accuracy over the RF algorithm. The improvement in classification accuracy can be as high as 40\% depending on the physical scales involved. We also investigate the ML algorithms’ ability to detect the impact of the speed of sound by choosing $c_s^2$ from the set $\{1, 10^{-2}, 10^{-4}, 10^{-7}\}$ while maintaining a constant $w_{\rm DE}$ for three different cases: $w_{\rm DE} \in \{-0.7, -0.8, -0.9\}$. Our results suggest that distinguishing between various values of $c_s^2$ and the case where $c_s^2=1$ is challenging, particularly at small scales and when $w_{\rm{DE}}\approx -1$. However, as we consider larger scales, the accuracy of $c_s^2$ detection improves. Notably, the CNN algorithm consistently outperforms the RF algorithm, leading to an approximate 20\% enhancement in $c_s^2$ detection accuracy in some cases.

یکشنبه23 اردیبهشت 1403، ساعت 17:00

Sunday 12 May 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 /Physics Department – first floor – Room Physics 3   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Mohammad Ansari

Department of Physics, K.N. Toosi University of Technology, Tehran, Iran;

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

The nearest neighbor statistics in cosmology

Abstract: The statistic of matter in non-linear regimes is non-Gaussian, and the two-point correlation function doesn’t have all the information in it. Introducing innovative quantities, along with the two-point correlation function is useful for non-linear regimes. In this direction we introduce the nearest neighbor statistics and show how this function could help us to constrain parameters and cosmological models (such as neutrino mass and fuzzy dark matter). In addition, for the first time we introduce the angle between nearest neighbors to cosmology. Noting that this quantity depends on angles and geometry (and not distances), exploring it may open up new horizons to cosmology. For example, by this quantity we can classify different cosmic web finder approaches.

یکشنبه16 اردیبهشت 1403، ساعت 17:00

Sunday 5 May 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Farnik Nikakhtar

Department of Physics, Yale University, USA

Year 1 results of the Dark Energy Spectroscopic Instrument with a focus on Baryon Acoustic Oscillations 

Abstract: The Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a five-year redshift survey of 40 million extragalactic sources across 14,000 square degrees of the northern sky, up to a redshift of 4, using the Mayall 4-meter telescope at Kitt Peak National Observatory. One of its primary goals is to precisely and accurately measure the cosmic expansion history through measurements of baryon acoustic oscillations (BAO). In this talk, I will discuss the measurements from DESI’s first-year Baryon Acoustic Oscillations, utilizing the distributions of galaxies (and quasars) over a redshift range of 0.1-2. For the first time, the DESI team employed catalog-level blinding in the BAO analysis to prevent confirmation bias in determining the expansion history. The resultant aggregate precision of the DESI Year 1 BAO analysis surpasses that of all previous galaxy surveys combined, prior to DESI.

یکشنبه  9 اردیبهشت 1403، ساعت 17:00

Sunday 28 April 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – آمفی تئاتر (تالار جناب) /Physics Department – Amphitheater  (Jenab Hall)   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Ebrahim Siri

Department of Physics, Sharif University of Technology

Thermodynamic properties of a relativistic Bose gas under rigid rotation

Abstract: The investigation of the impact of rotation on fermionic and bosonic systems has recently become a significant area of research in finite temperature field theory. In this work, we focus on a system of relativistic Bose gas subjected to a rigid rotation and analyze its thermodynamic properties. First, we introduce the rigid rotation metric and derive the solutions of the Klein-Gordon equation in cylindrical coordinates. We then calculate the propagator of a rotating bosonic system by making use of the generalized Fock-Schwinger proper-time method. Using the imaginary time formalism at finite temperature, we compute the thermodynamic potential of the system up to the first order of perturbative expansion. Additionally, we determine the nonperturbative ring contribution to the thermodynamic potential. Utilizing this potential, we calculate some thermodynamic quantities, such as pressure, energy density, entropy density, and angular momentum density. The obtained results show that the moment of inertia becomes negative in certain regimes of the parameter space. Our results are similar to the recent findings for the moment of inertia of a rotating gluonic plasma, where a supervortical temperature is introduced.

یکشنبه  2 اردیبهشت 1403، ساعت 17:00

Sunday 21 April 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3/  Physics Department – first floor – Room Physics 3    

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

گزینه ورود به صورت مهمان – Enter as a Guest

Bahar Nikbakht

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

Non-Gaussianity consistency relations and their consequences for the peaks

Abstract: Strong deviations from scale invariance and the appearance of high peaks in the primordial power spectrum have been extensively studied for generating primordial black holes (PBHs) or gravitational waves (GWs). It is also well-known that the effect of non-linearities can be significant in both phenomena. In this study, we introduce a general single-field consistency relation that relates the amplitude of non-Gaussianity in the squeezed limit  to the power spectrum and remains valid when almost all other consistency relations are violated.

Then we discuss the general and model-independent consequences of the consistency relation on the behavior of  at different scales.

As an implication of our results, we argue that non-linearities can shift or extend the range of scales responsible for the production of PBHs or GWs, relative to the window as determined by the largest peak of the power spectrum, and may also open up new windows for both phenomena.

یکشنبه 26 فروردین 1403، ساعت 17:00

Sunday 14 April 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 /Physics Department – first floor – Room Physics 3   

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

گزینه ورود به صورت مهمان – Enter as a Guest

Samaneh Sarbaz

Department of Physics, Sharif University of Technology

Seminar 1: Radio Astronomy: A brief report on the topics covered in the I_HOW/IAU radio astronomy workshop

Zahra Tabatabaee

Department of Physics, Sharif University of Technology

Seminar 2: The dynamics of FRW universe in scalar-Tensor-Vector gravity

Abstract 1: Today, radio astronomy is one of the best methods for observing the universe. A wide range of topics, such as star and planet formation, galaxy formation and evolution and interstellar and intergalactic medium can be ideally studied using these radio data. In September 2023,IAU/I-HOW Radio Astronomy was held at Erciyes University, Kayseri, Türkiye. One of the objectives of this Workshop was to prepare young researchers to learn how to analyse radio data from radio telescopes such as ALMA and VLA. In our upcoming talk, I will discuss radio astronomy. I am going to talk about the introduction of radio telescopes and analyzing radio data. This talk will be a brief report on the topics covered in the I_HOW/IAU radio astronomy workshop. 

Abstract 2: The Scalar-Tensor-Vector-Gravity (STVG), also known as MOG (Modified Gravity), has been proposed as a solution to the dark matter problem. In this talk, a gauge-invariant theory for MOG will be introduced through a symmetry-breaking mechanism at low temperatures, where gravitational attraction is governed by an effective gravitational constant. The modified Friedmann equation and scale factor evolution for this theory will be discussed. Finally, it will be mentioned that this theory has the potential to alter the dynamics of the early and late Universe.

یکشنبه 20 اسفند 1402، ساعت 17:00

Sunday 10 March 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3  / 

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

گزینه ورود به صورت مهمان – Enter as a Guest

Samira Cheraghchi

Department of Physics, University of Tehran

Four-dimensional SO(3)-spherically symmetric Berwald Finsler spaces

Abstract: Besides having an introduction to Finslerian geometry and its application in Physics, We locally classify all SO(3)-invariant four-dimensional pseudo-Finsler Berwald structures. These are Finslerian geometries which are closest to (spatially, or SO(3))-spherically symmetric pseudo-Riemannian ones — and serve as ansatz to find solutions of Finsler gravity equations which generalize the Einstein equations. We find that there exist five classes of non-pseudo-Riemannian (i.e. non-quadratic in the velocities) SO(3)-spherically symmetric pseudo-Finsler Berwald functions, which have either a heavily constrained dependence on the velocities, or, up to a suitable choice of the tangent bundle coordinates, no dependence at all on the “time” and “radial” coordinates. Also, we will present that in the cosmological symmetric case, the Finsler function only can have one non-trivial (non-Riemannian) form.

یکشنبه 13 اسفند 1402، ساعت 17:00

Sunday 3 March 2024 – 17:00 Tehran Time

Hybrid Seminar

دانشکده فیزیک – طبقه اول – کلاس فیزیک 3 Physics Department – first floor – Room Physics 3    /

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

گزینه ورود به صورت مهمان – Enter as a Guest