سمینار این هفته را آقای دکتر شهرام خسروی از دانشکده فیزیک دانشگاه خوارزمی ارائه  خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:

Dark Energy at Large Scales: Homogeneous or What?

Abstract: The Integrated Sachs Wolfe (ISW) cross correlation with the galaxy distribution in late time is a promising tool to constrain the dark energy properties. In this work we study the effect of dark energy clustering on the ISW-galaxy cross correlation. Indicating the fact that the bias parameter between the distribution of the galaxies and the underlying dark matter introduce a degeneracy and complications. We argue that as the time of the galaxy’s host halo formation is different from the observation time, we have to consider the evolution of the halo bias parameter. We indicate that any deviation from ΛCDM model will change the evolution of the bias as well. Also we show that the halo bias strongly depends on the sub-sample of galaxies which is chosen for cross correlation. We show that joint kernel of ISW effect and the galaxy distribution have the dominant effect on the observed signal, accordingly we can enhance the signal of a specific dark energy model by choosing an appropriate tracer. More specifically we compare the clustered dark energy models with two samples of galaxies. First is a sub-sample of galaxies from Sloan Digital chosen with the r-band magnitude 18<r<21 with a host dark matter halos of mass M∼1012M⊙ and formation redshift of z∼2.5. Secondly with the sub-sample of Luminous Red galaxies with a host dark matter halos of mass M∼1013M⊙ and formation redshift of z∼2.0. Using the evolved bias we improve the χ2 for the ΛCDM which it reconcile the ∼1-2σ tension of the ISW-galaxy signal and ΛCDM prediction. Finally we show how sub-samples change the bias parameter and will improve the constrains on dark energy clustering.

این سمینار در روز یکشنبه ۶ دی ماه ۱۳۹۴، ساعت ۱۵ در کلاس فیزیک ۴ در طبقه اول  دانشکدهٔ فیزیک برگزار خواهد شد.