Furkan Semih Dündar, Zahra Mirzaiyan, Metin Arik

We studied the gravitational collapse of a shell of dust in shape dynamics. We found out static and oscillatory solutions. In the large momentum limit we found out that the shell never reaches the singularity when the momentum of the shell is much larger than the mass of the shell in magnitude. The shell does not reach to the origin in a finite amount of time however when the momentum of the shell becomes comparable to minus the mass of shell, the large momentum approximation breaks down. Therefore more detailed future works hopefully may be able to answer the question of singularity formation in this setup.

A. A. Aguilar-Arevalo, B. C. Brown, L. Bugel, G. Cheng, E. D. Church, J. M. Conrad, R. L. Cooper, R. Dharmapalan, Z. Djurcic, D. A. Finley, R. S. Fitzpatrick, R. Ford, F. G. Garcia, G. T. Garvey, J. Grange, W. Huelsnitz, C. Ignarra, R. Imlay, R. A. Johnson, J. R. Jordan, G. Karagiorgi, T. Katori, T. Kobilarcik, W. C. Louis, K. Mahn, C. Mariani, W. Marsh, G. B. Mills, J. Mirabal, C. D. Moore, J. Mousseau, P. Nienaber, B. Osmanov, Z. Pavlovic, D. Perevalov, H. Ray, B. P. Roe, A. D. Russell, M. H. Shaevitz, J. Spitz, I. Stancu, R. Tayloe, R. T. Thornton, R. G. Van de Water, M. O. Wascko, D. H. White, D. A. Wickremasinghe, G. P. Zeller, E. D. Zimmerman

We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest ($K^+ \rightarrow \mu^+ \nu_\mu$) at the NuMI beamline absorber. These signal $\nu_\mu$-carbon events are distinguished from primarily pion decay in flight $\nu_\mu$ and $\overline{\nu}_\mu$ backgrounds produced at the target station and decay pipe using their arrival time and reconstructed muon energy. The significance of the signal observation is at the 3.9$\sigma$ level. The muon kinetic energy, neutrino-nucleus energy transfer ($\omega=E_\nu-E_\mu$), and total cross section for these events is extracted. This result is the first known-energy, weak-interaction-only probe of the nucleus to yield a measurement of $\omega$ using neutrinos, a quantity thus far only accessible through electron scattering.

Tejaswi Venumadhav, Liang Dai, Alexander Kaurov, Matias Zaldarriaga

The intergalactic medium is expected to be at its coldest point before the formation of the first stars in the universe. Motivated by recent results from the EDGES experiment, we revisit the standard calculation of the kinetic temperature of the neutral gas through this period. When the first ultraviolet (UV) sources turn on, photons redshift into the Lyman lines of neutral hydrogen and repeatedly scatter within the Lyman-$\alpha$ line. They heat the gas via atomic recoils, and, through the Wouthuysen-Field effect, set the spin temperature of the 21-cm hyperfine (spin-flip) line of atomic hydrogen in competition with the resonant cosmic microwave background (CMB) photons. We show that the Lyman-$\alpha$ photons also mediate energy transfer between the CMB photons and the thermal motions of the hydrogen atoms. In the absence of X-ray heating, this new mechanism is the major correction to the temperature of the adiabatically cooling gas ($\sim 10 \%$ at $z=17$), and is several times the size of the heating rate found in previous calculations. We also find that the effect is more dramatic in non-standard scenarios that either enhance the radio background above the CMB or invoke new physics to cool the gas in order to explain the EDGES results. The coupling with the radio background can reduce the depth of the 21-cm absorption feature by almost a factor of two relative to the case with no sources of heating, and prevent the feature from developing a flattened bottom. As an inevitable consequence of the UV background that generates the absorption feature, this heating should be accounted for in any theoretical prediction.

Surajit Paul, Abhirup Datta, Siddharth Malu, Prateek Gupta, Reju Sam John, Sergio Colafrancesco

We present the discovery of ringlike diffuse radio emission structures in the peripheral regions of the Bullet cluster 1E 0657$-$55.8. Ring formations are spanning between 1--3 Mpc away from the center of the cluster, significantly further away from the two already reported relics. Integrated fluxes of four of the sub-regions in the inner `ring' from 4.5 to 10 GHz have also been reported. To understand the possible origin of these structures, here we present a maiden attempt of numerical modelling of a 3D and realistic `bullet' like event in a full cosmological ($\Lambda$CDM) environment with N-body plus hydrodynamics code. We report a simulated `bullet' found inside a (128 Mpc)$^3$ volume simulation with a speed of 2700 km s$^{-1}$, creating a high supersonic bow shock of Mach $M=3.5$ and a clear evidence of temporal separation of dark matter and baryons, assuring no challenge to $\Lambda$CDM cosmology from the bullet event as of now. We are also able to unveil the physics behind the formation of these observed multiple shock structures. Modelled radio emissions in our simulation support a complex combination of merger-associated processes that accelerates and re-accelerates fossil and cosmic-ray electrons. With a time evolution study and the computed radio emissions, we have shown that the ring like formation around the bullet is originated due to the interaction of the strong merger shocks with the accretion shocks at the periphery. The multiple shock structures observed are possibly originated from multiple mergers that have taken place at different times and much before the bullet event.

Ariel Zhitnitsky

We advocate the idea that the nanoflares conjectured by Parker long ago to resolve the corona heating problem, may also trigger the larger solar flares. The arguments are based on the model where emission of extreme ultra violet (EUV) radiation and soft x-rays from the Sun are powered externally by incident dark matter particles within the Axion Quark Nugget (AQN) Dark Matter Model. The corresponding annihilation events of the AQNs with the solar material are identified with nanoflares. This model was originally invented as a natural explanation of the observed ratio $\Omega_{\rm dark} \sim \Omega_{\rm visible}$ when the DM and visible matter densities assume the same order of magnitude values. When the same nuggets enter the regions with high magnetic field they serve as the triggers igniting the magnetic reconnections which eventually may lead to much larger flares. Technically, the magnetic reconnection is ignited due to the shock wave which inevitably develops when the dark matter nuggets enter the solar atmosphere with velocity $v_{\rm AQN}\sim ~10^3 {\rm km/s}$ which is much higher than the speed of sound $c_s$, such that the Mach number $M=v_{\rm AQN}/c_s\gg 1$. These shock waves generate very strong and very short impulses expressed in terms of pressure $\Delta p/p\sim M^2$ and temperature $\Delta T/T\sim M^2$ in vicinity of (would be) magnetic reconnection area. We find that this mechanism is consistent with x -ray observations as well as with observed jet like morphology of the initial stage of the flares. The mechanism is also consistent with the observed scaling of the flare distribution $dN\sim W^{-\alpha}dW$ as a function of the flare's energy $W$. We also speculate that the same nuggets may trigger the sunquakes which are known to be correlated with large flares.