Magnetic Fields from Phase Transitions Tina Kahniashvili Mc

Magnetic Fields from Phase Transitions Tina Kahniashvili Mc. Williams Center for Cosmology Carnegie Mellon University & Abastumani Astrophysical Observatory Ilia State University Tbilisi 2015

Collaboration 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

Cosmic Magnetic Fields Earth MF Interstellar MF Galaxy MF Sun MF

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

Ultra High Energy Gamma Rays Tests u Gamma Ray map Neronov and Semikoz 2009 u u u Blazars The ultra high energy photons (gamma rays above 0. 1 Te. V) 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

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

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

Known - Unknown u What we know: u • The amplitude of the magnetic field • The spectral shape of the magnetic field • The 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

Why Cosmological Magnetic Fields are attractive? u u u 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

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

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

Cosmological Magnetic Fields u BBN limits: 10% of additional relativistic component • 0. 1 – 1 micro. Gauss (comoving value) u Faraday Rotation Measure • At z~2 -3 micro. Gauss • Initial pico. Gauss?

Phenomenology u 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

Phase Transitions Generated Magnetic Field Phenomenology Kahniashvili, Tevzadze, Brandenburg, Neronov 2012 u u Non-helical field Helical field • Helicity conservation law

MHD Simulations Brandenburg, Kahniashvili, Tevzadze, 2014

Modeling Magnetic Field

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

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

Results Kahniashvili, Tevzadze, Brandenburg, Neronov 2012

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

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

High Resolution MHD Simulations Brandenburg, Kahniashvili, Tevzadze 2015 u u u 23043 meshpoints on 9216 processors Runs A and B with magnetic Prandtl numbers = 1 and 10 Non-helical magnetic fields u Intermediate region: Iroshnikov-Kraichnan Goldreich-Sridhar Weak-turbulence

Energies Cascades u Non-helical magnetic fields • Forward cascade u Helical magnetic fields • Inverse cascade We have shown the inverse transfer for non-helical fields

Inverse Transfer Brandenburg, Kahniashvili, Tevzadze 2014

Brandenburg, Kahniashvili, Tevzadze 2014

Brandenburg, Kahniashvili, Tevzadze 2014

Brandenburg, Kahniashvili, Tevzadze 2014

Nonhelical Magnetic Fields Decay Brandenburg, Kahniashvili, Tevzadze 2014

Helical Magnetic Fields Decay Brandenburg, Kahniashvili, Tevzadze 2015

Helical Magnetic Fields Decay Brandenburg, Kahniashvili, Tevzadze 2015 Causal fields – correlation length limitation un. B=2 or n. B=0 Inverse Cascade

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

Helical Magnetic Fields Scaling Laws Brandenburg, Kahniashvili, Tevzadze 2015

Helical Magnetic Field Brandenburg, Kahniashvili, Tevzadze 2015

Classes of Turbulence Brandenburg & Kahniashvili, 2015

Conclusion u u 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