Superradiance effects in General Relativity Introduction to - - PowerPoint PPT Presentation
Superradiance effects in General Relativity Introduction to Gravitational Waves Emmanuele Picciau A.A. 2017/2018 Summary What is
Introduction to Gravitational Waves
Emmanuele Picciau A.A. 2017/2018
Superradiance is the radiation enhancement effect based on the dissipation of a physical system. Superradiance examples:
Sonic «boom» Superradiance amplification of sound waves
Cherenkov radia iation Superradiance amplification of electromagnetic waves
Coherent emit itters If there are N emitters the intensity of the radiation is: ∝ 𝑂 for incoherent regime ∝ 𝑂2 for coherent regime
Rotational superradiance In 1971 Zel’dovich showed that when radiation scatter off rotating absorbing surface it could increase its amplitude if ω: frequency of the radiation Ω: orbital velocity of the body m: azimutal number
One of the first examples of superradiance is known as the Kle lein in paradox A particle beam propagating in a region with a potential barrier V can emerge without exponential damping
Klein, O. Z. Physik (1929) 53: 157. https://doi.org/10.1007/BF01339716
The paradox is today resolved by the creation of pair ir particle-antiparticle le Klein-Gordon and Dirac equations are not 1-particle equations, but relativistic field equations
Bosonic scattering Fermionic scatterin ing
Where:
For bosons the solution of the problem is so, under the condition is possible to have superradiant amplification of the reflected current
Let’s consider a scalar field 𝜚 around a spinning body In a coordinate system in which the medium is at rest: 𝛽: absorption parameter
Superradia iance from stars
In astrophysics superradiance amplification of radiation comes by the extraction of energy from massive objects This effect could be the cause of instabilities of systems
CFS in instabil ility
The instability occurs when a mode that is retrograde in the frame corotating with the star appears as prograde to a inertial frame.
Bla lack Hole le bombs If we have a scalar perturbing a rotating axis-symmetric black hole Let’s imagine to enclose the black hole in a reflecting mirror
In Instabilit ity from bosonic massiv ive fie ield ld «Nature provide its own mirrors»
In Instabilit ity from bosonic massiv ive fie ield ld If the imaginary part becomes positive can be defined an instability time scale In this case the field could growth as
Phys.Rev. D86 (2012) 104017, arXiv:1209.0773
Superradiant instability for the fundamental mode (l=m=1) as a function of the coupling Mμs and for several spinning BHs In Instabilit ity from bosonic massiv ive fie ield ld
In the instabilities time scale τ a cloud of bosons could grow near the BH Backreaction on the geometry caused by bosons is neglected
Evolution of f in instabilities
Using Teukolsky formalism
Emission of f en energy and angular momentum
instabilities," arXiv:1411.0686
Bosenova and emission of f GWs
Hirotaka Yoshino and Hideo Kodama 2015 Class. Quantum Grav. 32 214001
Scattering and absorption of f gr gravitational pla lane waves by rotating BHs BHs
Class.Quant.Grav. 25 (2008) 235002, arXiv:0801.3805
We have seen how superradiance effects could modify the dynamics of classical and quantum physical systems.
dissipative systems.
consequences about physics beyond the Standard Model
their parameters