High Energy Physics Seminar

[Rosanna]

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HIGH ENERGY PHYSICS SEMINAR
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TUESDAY, 22 SEPTEMBER 2020, 14:30 p.m.



Tina KAHNIASHVILI
(Carnegie Mellon University, USA and Ilia State University, Georgia)



"Circular polarization of gravitational waves from the early-universe 
turbulent sources"


Abstract:A space-based laser interferometer, pioneered by NASA's LISA 
concept and now a ESA cornerstone mission, will enable direct detection 
of gravitational waves at lower frequencies than LIGO, without being 
limited by seismic noise. Perhaps the most intriguing source for LISA is 
the stochastic gravitational wave background produced by turbulent 
plasma motions in an early-universe, particularly at the electroweak 
energy scale. In this talk I will discuss the stochastic gravitational 
wave background generated from early-universe turbulence, including the 
effects of possible parity violation which will result in the non-zero 
circular polarization. Turbulent sources possibly present at the 
electroweak energy scales produce gravitational waves with a 
characteristic frequency of a millihertz, squarely in LISA's sensitivity 
window. I will present our recent results (in collaboration with Axel 
Brandenburg, Arthur Kosowsky, Sayan Mandal and Alberto Roper Pol) 
of direct numerical simulations to compute the net circular polarization 
of gravitational waves from helical (chiral) turbulent sources in the 
early universe for a variety of initial conditions. I will discuss the 
resulting gravitational wave signal assuming different turbulence 
genesis such as magnetically or kinetically dominant cases. Under 
realistic physical conditions in the early universe we have computed 
numerically for the first time the total polarization degree of the 
gravitational waves and its spectral distribution. Our major finding 
consists of the spectral polarization degree that strongly depends on 
the initial conditions. The peak of the spectral polarization degree 
occurs (in the wavenumber space) at twice the typical wavenumber of the 
source, as expected, and for the fully helical decaying turbulence, 
reaches its maximum (100\%) only at the peak. In addition, we have 
determined the temporal evolution of the turbulent sources as well as 
the resulting gravitational waves, showing that the dominant 
contribution to the spectral energy density happens shortly after the 
source activation and through prolonged (slow decay) turbulence, the 
increase of the gravitational wave amplitude at low frequencies can be 
achieved. Finally, I will address the detection prospects through LISA 
for the gravitational wave signal and its net polarization.


Please register in advance for this meeting:

https://zoom.us/meeting/register/tJIsf-yurDkrHNG5jcghEWy832HK97baZSnL


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the meeting.


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