1. Magnetic Fields from Phase Transitions Magnetic Fields from Phase Transitions Tina Kahniashvili McWilliams Center for Cosmology Carnegie Mellon University & Abastumani Astrophysical Observatory Ilia State University Tbilisi 2015 TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAA

2. Axel Brandenburg, NORDITA, Sweden Andrii Neronov, Geneva University, Switzerland Bharat Ratra, Kansas State University, USA Alexander Tevzadze, Tbilisi State University, Georgia Tanmay Vachaspati, Arizona State University, USA Collaboration

3. Cosmic Magnetic Fields Sun MF Galaxy MF Earth MF Interstellar MF

4. Magnetic Helicity Magnetic Helicity Magnetic helicity reflects mirror symmetry (parity) breaking Solar activity: Sunspots Solar flares Coronal mass ejection Solar wind

5. Ultra High Energy Gamma Rays Tests   Gamma Ray map   Blazars  The ultra high energy photons (gamma rays above 0.1 TeV) interact with the diffuse extragalactic background light  If the magnetic field along the path of the cascade production is strong enough to bend the pair trajectories then the cascade emission appears as an extended halo around the initial point source Neronov and Semikoz 2009

6. Gamma Rays vs Magnetic Fields Tashiro, Chen, Francesc, Vachaspati 2014 Neronov and Vovk 2010

7. Cosmic Magnetic Fields Some History E. Fermi “On the origin of the cosmic radiation”, PRD, 75, 1169 (1949)

8. Known - Unknown   What we know: The amplitude of the magnetic fieldThe amplitude of the magnetic field The spectral shape of the magnetic fieldThe spectral shape of the magnetic field The correlation length scaleThe correlation length scale  What we do not know: When and how magnetic fields were generated What were initial conditions Two Options: Cosmological and Astrophysical Scenarious

9. Are the observed magnetic fields of a primordial origin  Might serve as seeds for the observed fields in galaxies and clusters  Might be responsible for large scale correlated magnetic fields in the voids  Might explain some cosmological observations Why Cosmological Magnetic Fields are attractive?

10. Cosmological vs. Astrophysical Magnetogenesis MHD Simulations by Donnert et al. 2008 Z=4 Z=0 Z=4 Z=0 Ejection Primordial

11. Primordial Magnetic Field Hypothesis F. Hoyle in Proc. “La structure et l’evolution de l’Universe” (1958)  Inflation  Phase transitions  Supersymmetry  String Cosmology  Topological defects  Phase Transitions Bubble collisions – first order phase transitions  QCDPT  EWPT Causal fields Limitation of the correlation length  Smoothed and effective fields approaches

12. Cosmological Magnetic Fields  BBN limits: 10% of additional relativistic component 0.1 – 1 microGauss0.1 – 1 microGauss (comoving value)  Faraday Rotation Measure At z~2-3 microGauss Initial picoGauss?

13. Phenomenology  If the magnetic field has been generated through a causal process in the early Universe it’s correlation length could not exceed the Hubble horizon at the moment of the generation

14.  Non-helical field  Helical field Helicity conservation lawHelicity conservation law Phase Transitions Generated Magnetic Field Phenomenology Kahniashvili, Tevzadze, Brandenburg, Neronov 2012

15. MHD Simulations Brandenburg, Kahniashvili, Tevzadze, 2014

16. Modeling Magnetic Field

17. MHD Modeling  Coupling of the magnetic field with primordial plasma  Injection of the magnetic energy at a given scale (phase transition bubble) Kahniashvili, Brandenburg, Ratra, Tevzadze 2010

18.   We recover k 4 spectrum at large scales for both – helical and non-helical PMF   Initial Conditions for the decay stage were prepared through forced case   The velocity field at large scales is described by white noise Magnetic Field Spectrum Kahniashvili, Tevzadze, Brandenburg, Neronov 2012

21. Results Kahniashvili, Tevzadze, Brandenburg, Neronov 2012

22. Magnetic field from QCD Phase Transitions Tevzadze, Kisslinger, Brandenburg, Kahniashvili 2012

23. Magnetic Helicity Growth Tevzadze, Kisslinger, Brandenburg, Kahniashvili 2012  The correlation length should satisfy:  Magnetic helicity grows until it reaches its maximal value

24. High Resolution MHD Simulations  2304 3 meshpoints on 9216 processors  Runs A and B with magnetic Prandtl numbers = 1 and 10  Intermediate region: Iroshnikov-Kraichnan Goldreich-Sridhar Weak-turbulence  Non-helical magnetic fields Brandenburg, Kahniashvili, Tevzadze 2015

25. Energies Cascades  Non-helical magnetic fields Forward cascadeForward cascade  Helical magnetic fields Inverse cascade We have shown the inverse transfer for non-helical fields

26. Inverse Transfer Brandenburg, Kahniashvili, Tevzadze 2014

30. Nonhelical Magnetic Fields Decay

31. Brandenburg, Kahniashvili, Tevzadze 2015 Helical Magnetic Fields Decay

32. Brandenburg, Kahniashvili, Tevzadze 2015 Causal fields – correlation length limitation  n B =2 or n B =0 Inverse Cascade

33. Inflation Generated Helical Magnetic Field Kahniashvili, Durrer, Brandenburgh, Tevzadze 2015 The absence of inverse cascade for Inflation generated magnetic fields

34. Helical Magnetic Fields Scaling Laws Brandenburg, Kahniashvili, Tevzadze 2015

35. Helical Magnetic Field Brandenburg, Kahniashvili, Tevzadze 2015

36. Classes of Turbulence Brandenburg & Kahniashvili, 2015

37. Conclusion  The lower bound of the extragalactic magnetic field favors a primordial (phase transitions) magnetogenesis approach (in particular, helical magnetic fields)  The primordial magnetic field might be a plausible explanation for the galaxy magnetic field