Three-dimensional simulations of the interaction between Type Ia supernova ejecta and their main sequence companions
The identity of the progenitor systems of Type Ia supernovae (SNe Ia) is still uncertain. In the single-degenerate scenario, the interaction between the supernova blast wave and the outer layers of a main sequence companion star strips off hydrogen-rich material which is then mixed into the ejecta. Strong contamination of the supernova ejecta with stripped material could lead to a conflict with observations of SNe Ia. This constrains the single-degenerate progenitor model.  In this work, our previous simulations based on simplified progenitor donor stars have been updated by adopting more realistic progenitor-system models that result from fully detailed, state-of-the-art binary evolution calculations.  We use Eggleton's stellar evolution code including the optically thick accretion wind model and taking into account the possibility of the effects of accretion disk instabilities to obtain realistic models of companion stars for different progenitor systems. The impact of the supernova blast wave on these companion stars is followed in three-dimensional hydrodynamic simulations employing the smoothed particle hydrodynamics code GADGET3.  For a suite of main sequence companions, we find that the mass of the material stripped from the companions range from 0.11 M-circle dot to 0.18 M-circle dot. The kick velocity delivered by the impact is between 51 km s(-1) and 105 km s(-1). We find that the stripped mass and kick velocity depend on the ratio of the orbital separation to the radius of a companion, a(f)/R. They can be fitted in good approximation by a power law for a given companion model. However, we do not find a single power law relation holding for different companion models. This implies that the structure of the companion star is also important for the amount of stripped material.  With more realistic companion star models than those employed in previous studies, our simulations show that the hydrogen masses stripped from companions are inconsistent with the best observational limits (<= 0.01 M-circle dot) derived from SN Ia nebular spectra. However, a rigorous forward modeling from the results of impact simulations with radiation transfer is required to reliably predict observable signatures of the stripped hydrogen and to conclusively assess the viability of the considered SN Ia progenitor scenario.

title: Rotation of surviving companion stars after type Ia supernova explosions in the WD+MS scenario
abstract: In the single-degenerate (SD) scenario of type Ia supernovae (SNe Ia) the non-degenerate companion star survives the supernova (SN) explosion and thus should be visible near the center of the SN remnant and may show some unusual features. Therefore, a promising approach to test progenitor models of SNe Ia is to search for the companion star in historical SN remnants.  Here we present the results of three-dimensional (3D) hydrodynamics simulations of the interaction between the SN Ia blast wave and a main-sequence companion taking into consideration its orbital motion and spin. The primary goal of this work is to investigate the rotation of surviving companion stars after SN Ia explosions in the WD+MS scenario.  We used Eggleton's stellar evolution code including the optically thick accretion wind model to obtain realistic models of companion stars. The impact of the supernova blast wave on these companion stars was followed in 3D hydrodynamic simulations employing the smoothed particle hydrodynamics (SPH) code GADGET3.  We find that the rotation of the companion star does not significantly affect the amount of stripped mass and the kick velocity caused by the SN impact. However, in our simulations, the rotational velocity of the companion star is significantly reduced to about 14% to 32% of its pre-explosion value due to the expansion of the companion and because 55%-89% of the initial angular momentum is carried away by the stripped matter.  Compared with the observed rotational velocity of the presumed companion star of Tycho's supernova, Tycho G, of similar to 6 km s(-1), the final rotational velocity we obtain in our simulations is still higher by at least a factor of two. Whether this difference is significant and may cast doubts on the suggestion that Tycho G is the companion of SN 1572 has to be investigated in future studies. Based on binary population synthesis results, we present for the first time the expected distribution of rotational velocities of companion stars after the SN explosion, which may provide useful information for the identification of the surviving companion in observational searches in other historical SN remnants.

title: Sparticles at the LHC
abstract: Sparticle mass hierarchies will play an important role in the type of signatures that will be visible at the Large Hadron Collider. We analyze these hierarchies for the four lightest sparticles for a general class of supergravity unified models including nonuniversalities in the soft breaking sector. It is shown that out of nearly 104 possibilities of sparticle mass hierarchies, only a small number survives the rigorous constraints of radiative electroweak symmetry breaking, relic density and other experimental constraints. The signature space of these mass patterns at the Large Hadron Collider is investigated using a large set of final states including multi-leptonic states, hadronically decaying τs, tagged b jets and other hadronic jets. In all, we analyze more than 40 such lepton plus jet and missing energy signatures along with several kinematical signatures such as missing transverse momentum, effective mass, and invariant mass distributions of final state observables. It is shown that a composite analysis can produce significant discrimination among sparticle mass patterns allowing for a possible identification of the source of soft breaking. While the analysis given is for supergravity models, the techniques based on mass pattern analysis are applicable to wide class of models including string and brane models.

title: Observation of the decay psi(2S) ---> K*(892)anti-K + c.c.

title: Renormalization of bilinear quark operators for overlap fermions
abstract: We present nonperturbative renormalization constants of fermionic bilinears on the lattice in the quenched approximation at {beta}=6.1 using an overlap [H. Neuberger,  (1998)] fermion action with hypercubic (HYP)-blocked links. We consider the effects of the exact zero modes of the Dirac operator and find they are important in calculating the renormalization constants of the scalar and pseudoscalar density. The results are given in the RI' and MS schemes and compared to perturbative calculations.

title: Hidden Sector Models and Signatures
abstract: In the Stueckelberg extension of the Standard Model (StSM), matter in the hidden sector can act as dark matter. Due to an interplay of mixings produced by the usual Higgs mechanism and the Stueckelberg mechanism in the neutral gauge boson sector, the hidden sector matter acquires a milli charge. The Stueckelberg extension also produces a narrow width Z prime which is detectable at the Large Hadron Collider. The hidden sector dark matter naturally explains the PAMELA positron excess by means of a Breit-Wigner enhancement through a Z prime resonance. We also discuss the origin of milli charge in the context of the kinetic mixing and the Stueckelberg mixing.

title: The Stueckelberg Z prime at the LHC: discovery potential, signature spaces and model discrimination
abstract: An analysis is given of the capability of the LHC to detect narrow resonances using high luminosities and techniques for discriminating among models are discussed. The analysis is carried out with focus on the U(1)X Abelian (Higgless) Stueckelberg extension of the Standard Model (StSM) gauge group which naturally leads to a very narrow Z' resonance. Comparison is made to another class of models, i.e., models based on the warped geometry which also lead to a narrow resonance via a massive graviton (G). Methods of distinguishing the StSM Z' from the massive graviton at the LHC are analyzed using the dilepton final state in the Drell-Yan process pp?Z'?l+l? and pp?G?l+l?. It is shown that the signature spaces in the ?.Br(l+l?)-resonance mass plane for the Z prime and for the massive graviton are distinct. The angular distributions in the dilepton C-M system are also analyzed and it is shown that these distributions lie high above the background and are distinguishable from each other. A remarkable result that emerges from the analysis is the observation that the StSM model with Z' widths even in the MeV and sub-MeV range for Z' masses extending in the TeV region can produce detectable cross section signals in the dilepton channel in the Drell-Yan process with luminosities accessible at the LHC. While the result is derived within the specific StSM class of models, the capability of the LHC to probe models with narrow resonances in this range may hold more generally.