سمینار این هفته را آقای دکتر یاشار اکرمی از موسسه فیزیک نظری دانشگاه هایدلبرگ ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:

Theoretical and observational challenges of gravity beyond Einstein:

A case study with massive (bimetric) gravity

Abstract: I will start with a brief overview of the successes and problems of the standard theory of gravity, mostly in the cosmological context, and will discuss various reasons why one needs to go beyond this standard framework. I will then review popular recipes to extend or modify gravity in a consistent way, and proceed with prospects for tests of the modified theories of gravity using near-future cosmological experiments such as Euclid and the SKA. The rest of my talk will focus on one of the most popular, theoretically well motivated, and mathematically consistent such modifications, namely theories of massive, bi- and multi-metric gravity and their cosmological implications. This has a long story and proved to be a very interesting but highly challenging modification which perfectly shows the difficulties in constructing alternative theories and confronting them with observations. Bimetric gravity, despite its theoretically strong motivations and cosmologically fascinating implications, in particular as an alternative explanation of the late-time acceleration of the Universe, has been widely argued to be plagued by severe (ghost and/or gradient instability) problems. I will argue in this talk that there are several possibilities to save the theory and obtain healthy cosmological solutions with implications which may or may not differ significantly from the standard cosmological picture when the predictions of the theory are compared to observations. I will illustrate that in either case the underlying physical mechanism behind the cosmic acceleration is theoretically of a completely different nature which provides a neat solution to the new cosmological constant (dark energy) problem in a technically natural way.

این سمینار در روز یکشنبه ۲۵ امرداد ماه ۱۳۹۴، ساعت ۱۰ در کلاس فیزیک ۳ در طبقهٔ اول  دانشکدهٔ فیزیک برگزار خواهد شد.