3255138
New Aspects and Boundary Conditions of Core-Collapse Supernova Theory
Core-collapse supernovae are among Nature’s grandest explosions. They are powered by 
the energy released in gravitational collapse and include a rich set of physical phenomena 
involving all fundamental forces and many branches of physics and astrophysics. We 
summarize the current state of core-collapse supernova theory and discuss the current set 
of candidate explosion mechanisms under scrutiny as core-collapse supernova modeling is 
moving towards self-consistent three-dimensional simulations. Recent work in nuclear theory 
and neutron star mass and radius measurements are providing new constraints for the 
nuclear equation of state. We discuss these new developments and their impact on corecollapse 
supernova modeling. Neutrino-neutrino forward scattering in the central regions 
of core-collapse supernovae can lead to collective neutrino flavor oscillations that result in 
swaps of electron and heavy-lepton neutrino spectra. We review the rapid progress that 
is being made in understanding these collective oscillations and their potential impact on 
the core-collapse supernova explosion mechanism.
5467110
Galactic center radio constraints on gamma-ray lines from dark matter annihilation
Recent evidence for one or more gamma-ray lines at ~ 130 GeV in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to Z{\gamma} or H{\gamma} with an annihilation cross section, ~ 10^{-27} cm^3 s^{-1} . We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from the decay of the Z or the H boson only in the Galactic Center against radio data from the same region in the Galactic Center. We find that the radio data from single dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes such as LWA, VLA-Low and LOFAR, and future radio telescopes like SKA, which are sensitive to annihilation cross sections as small as 10^{-28} cm^3 s^{-1}, can confirm or rule out this scenario very soon. We discuss the assumptions on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to Z{\gamma} or H{\gamma}.
199674547
Collective three-flavor oscillations of supernova neutrinos
We present a formalism to study three-flavor effects in flavor conversions of dense neutrino ensembles. The main idea is to use the smallness of Δm2⊙Δm2atm and θ13. The formalism has immediate applications to neutrinos from supernovae or the early Universe. We outline some consequences for supernova neutrino phenomenology, e.g hierarchy determination at extremely small θ13.
118571843
Effect of collective neutrino oscillations on the neutrino mechanism of core-collapse supernovae
In the seconds after collapse of a massive star, the newborn protoneutron star (PNS) radiates neutrinos of all flavours. The absorption of electron-type neutrinos below the radius of the stalled shockwave may drive explosions (the ‘neutrino mechanism’). Because the heating rate is proportional to the square of neutrino energy, flavour conversion of μ and τ neutrinos to electron-type neutrinos via collective neutrino oscillations (CνO) may in principle increase the heating rate and drive explosions. In order to assess the potential importance of CνO for the shock revival, we solve the steady-state boundary value problem of spherically symmetric accretion between the PNS surface (rν) and the shock (rS), including a scheme for flavour conversion via CνO. For a given rν, PNS mass (M), accretion rate () and assumed values of the neutrino energies from the PNS, we calculate the critical neutrino luminosity above which accretion is impossible and explosion results. We show that CνO can decrease the critical luminosity by a factor of at most ∼1.5, but only if the flavour conversion is fully completed inside rS and if there is no matter suppression. The magnitude of the effect depends on the model parameters (M, and rν) through the shock radius and the physical scale for flavour conversion. We quantify these dependencies and find that CνO could lower the critical luminosity only for small M and , and large rν. However, for these parameter values CνO are suppressed due to matter effects. By quantifying the importance of CνO and matter suppression at the critical neutrino luminosity for explosion, we show in agreement with previous studies that CνO are unlikely to affect the neutrino mechanism of core-collapse supernovae significantly.
124887197
Nonlinear Oscillations of Supernova Neutrinos
Declaration This thesis is a presentation of my original research work. Wherever contributions of others are involved, every effort is made to indicate this clearly, with due reference to the literature, and acknowledgement of collaborative research and discussions. In my capacity as supervisor of the candidate's thesis, I certify that the above statements are true to the best of my knowledge. iii Acknowledgements As I submit this thesis, I feel compelled to express my gratitude to many people. Foremost, I gratefully acknowledge the guidance and support that I have recieved from Prof. Amol Dighe, my thesis advisor. I also thank my collaborators for a pleasant and satisfying experience of working together. I would like to express my gratitude to my teachers from Jadavpur University who inspired me to study physics. The faculty at TIFR have all been very helpful and friendly and I thank them for enjoyable and exciting courses, and stimulating discussions. Thanks are due to the DTP office staff and the institute administration staff for their help and unsurpassable efficiency in sorting out every trouble I took to them. I acknowledge the financial support recieved from Max Planck India Partner Group and from TIFR. I also wish to take this opportunity to convey my love and regards for my parents and my brother. Without their encouragement I could not have come this far. And finally, my heartfelt gratitude to all my friends, who made these years absolutely delightful. v Foreword The cosmos has remained a favorite laboratory to test the laws of fundamental physics-tests of the laws of gravity being the most well-known example. However, over the last century we have progressed from merely charting the gross motion of astrophysical objects, to observing more subtle phenomena associated with them. Many of these phenomena depend crucially on the laws of particle physics. As a result, astrophysics and particle physics are now connected more intimately than ever, with a promise to yield valuable insights into the laws of Nature. Neutrinos, being ubiquitous and weakly interacting, explore regions that are out of bounds to other particles, and are an ideal candidate to probe this deep connection. Our knowledge of neutrinos has seen a revolution of sorts in the last few decades, thanks to a number of experiments on atmospheric, solar and terrestrial neutrinos. These experiments lead us to believe that there are three flavors of massive neutrinos ν e , ν …
31519375
Multiple spectral splits of supernova neutrinos.
Collective oscillations of supernova neutrinos swap the spectra f(nu(e))(E) and f(nu[over ](e))(E) with those of another flavor in certain energy intervals bounded by sharp spectral splits. This phenomenon is far more general than previously appreciated: typically one finds one or more swaps and accompanying splits in the nu and nu[over ] channels for both inverted and normal neutrino mass hierarchies. Depending on an instability condition, swaps develop around spectral crossings (energies where f(nu(e))=f(nu(x)), f(nu[over ](e))=f(nu[over ](x)) as well as E-->infinity where all fluxes vanish), and the widths of swaps are determined by the spectra and fluxes. Washout by multiangle decoherence varies across the spectrum and splits can survive as sharp spectral features.
32178161
Exclusion of Tiny Interstellar Dust Grains From the Heliosphere
The distribution of interstellar dust grains (ISDG) observed in the Solar System depends on the nature of the interstellar medium‐solar wind interaction. The charge of the grains couples them to the interstellar magnetic field (ISMF) resulting in some fraction of grains being excluded from the heliosphere while grains on the larger end of the size distribution, with gyroradii comparable to the size of the heliosphere, penetrate the termination shock. This results in a skewing the size distribution detected in the Solar System. 
 
We present new calculations of grain trajectories and the resultant grain density distribution for small ISDGs propagating through the heliosphere. We make use of detailed heliosphere model results, using three‐dimensional (3‐D) magnetohydrodynamic/kinetic models designed to match data on the shape of the termination shock and the relative deflection of interstellar H° and He° flowing into the heliosphere. We find that the necessary inclination of the ISMF relative to the inflow direction results in an asymmetry in the distribution of the larger grains (0.1 μm) that penetrate the heliopause. Smaller grains (0.01 μm) are completely excluded from the Solar System at the heliopause.
18721076
A practical approach to coronal magnetic field extrapolation based on the principle of minimum dissipation rate
We present a newly developed approach to solar coronal magnetic field extrapolation from vector magnetograms, based on the principle of minimum dissipation rate (MDR). The MDR system was derived from a variational problem that is more suitable for an open and externally driven system, like the solar corona. The resulting magnetic field equation is more general than force-free. Its solution can be expressed as the superposition of two linear (constant-α) force-free fields (LFFFs) with distinct α parameters, and one potential field. Thus, the original extrapolation problem is decomposed into three LFFF extrapolations, utilizing boundary data. The full MDR-based approach requires two layers of vector magnetograph measurements on the solar surface, while a slightly modified practical approach only requires one. We test both approaches against three-dimensional MHD simulation data in a finite volume. Both yield quantitatively good results. The errors in the magnetic energy estimate are within a few percent. In particular, the main features of relatively strong perpendicular current density structures, representative of the non-force-freeness of the solution, are well recovered.