Signals of a superlight gravitino at the LHC
A bstractVery light gravitinos could be produced at a sizeable rate at colliders and have been searched for in the mono-photon or mono-jet plus missing momentum signature. Strategies for enhancing the signal over background and interpretations of the experimental results are typically obtained within an effective field theory approach where all SUSY particles except the gravitino are heavy and are not produced resonantly. We extend this approach to a simplified model that includes squarks and gluinos in the TeV range. In such a case, the jet(s)-plus-missing-momentum signature can be generated through three different concurring mechanisms: gravitino-pair production with an extra jet, associated gravitino production with a squark or a gluino, or squark/gluino pair production with their subsequent decay to a gravitino and a jet. By using a matrix-element parton-shower merging procedure, we take into account all the relevant production processes consistently, explore the SUSY parameter space with the LHC Run-I data set, and give prospects for the Run II. We also consider the reach of other signatures involving electroweak particles, e.g., the mono-photon, -Z, or -W plus missing momentum. The current mono-jet and mono-photon LHC analyses are interpreted to set a lower bound on the gravitino mass. We show how the limit of m3/2> 1.7 × 10−13 GeV obtained in the effective field theory hypothesis is modified when the squarks and/or the gluino are in the TeV range.

title: Collider signatures of goldstini in gauge mediation
abstract: A bstractWe investigate the collider signatures of the multiple goldstini scenario in the framework of gauge mediation. This class of models is characterized by a visible sector (e.g. the MSSM or any extension) coupled by gauge interactions to more than one SUSY breaking sector. The spectrum consists of a light gravitino LSP, behaving as a goldstino, and a number of neutral fermions (the pseudo-goldstini) with a mass between that of the LSP and that of the lightest particle of the observable sector (LOSP). We consider the two situations where the LOSP is either a gaugino-like neutralino or a stau and we assume only one pseudo-goldstino of a mass of $ \mathcal{O}\left( {100} \right) $ GeV. The coupling of the LOSP to the pseudo-goldstino can be enhanced with respect to those of the gravitino giving rise to characteristic signatures. We show that the decay modes of the LOSP into a SM particle and a pseudo-goldstino can be significant. For both LOSP scenarios we analyze (pseudo)-goldstini production at colliders. Compared to standard gauge mediation the final state spectrum is softer and more structured.

title: TauDecay: a library to simulate polarized tau decays via FeynRules and MadGraph5
abstract: TauDecay is a library of helicity amplitudes to simulate polarized tau decays, constructed in the FeynRules and MadGraph5 framework. Together with the leptonic mode, the decay library includes the main hadronic modes, τ→ντ+π, 2π, and 3π, which are introduced as effective vertices by using FeynRules. The model file allows us to simulate tau decays when the on-shell tau production is kinematically forbidden. We also demonstrate that all possible correlations among the decay products of pair-produced taus through a Z boson and a scalar/pseudoscalar Higgs boson are produced automatically. The program has been tested carefully by making use of the standard tau decay library Tauola.

title: Simulating spin-$\frac{3}{2}$ particles at colliders
abstract: Support for interactions of spin-$\frac{3}{2}$ particles is implemented in the FeynRules and ALOHA packages and tested with the MadGraph 5 and CalcHEP event generators in the context of three phenomenological applications. In the first, we implement a spin-$\frac{3}{2}$ Majorana gravitino field, as in local supersymmetric models, and study gravitino and gluino pair-production. In the second, a spin-$\frac{3}{2}$ Dirac top-quark excitation, inspired from compositeness models, is implemented. We then investigate both top-quark excitation and top-quark pair-production. In the third, a general effective operator for a spin-$\frac{3}{2}$ Dirac quark excitation is implemented, followed by a calculation of the angular distribution of the s-channel production mechanism.

title: HELAS and MadGraph with spin-3/2 particles
abstract: Fortran subroutines to calculate helicity amplitudes with massive spin-3/2 particles, such as massive gravitinos, which couple to the standard model and supersymmetric particles via the supercurrent, are added to the HELAS (HELicity Amplitude Subroutines) library. They are coded in such a way that arbitrary amplitudes with external gravitinos can be generated automatically by MadGraph, after slight modifications. All the codes have been tested carefully by making use of the gauge invariance of the helicity amplitudes.

title: Decay distribution of tau produced by neutrino-nucleon scattering☆
abstract: We studied the decay distributions of τ leptons produced in neutrino-nucleon scattering via charged current interaction, taking into account the τ polarization, for the long baseline neutrino oscillation experiments which aim to observe ν τ appearance. The information on the τ polarization is essential for measuring ν τ appearance since the decay particle distributions depend crucially on the τ spin. We show that τ produced via neutrino has high degree of polarization, and its spin direction depends non-trivially on the energy and the scattering angle of τ in the laboratory frame. We also show that the subsequent decay distributions are significantly affected by the produced τ polarization.

title: An H-alpha search for over-dense regions at z=2.23
abstract: We present the results of a narrow-band (H2S1, 2.121/0.021um) imaging search with WFCAM/UKIRT for H-alpha emitters around several potential signposts of rare (10^-7-10^-8 Mpc^-3) over-dense regions at z=2.23: an over-density of QSOs (2QZ cluster), a powerful, high-redshift radio galaxy (HzRG), and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrow-band emitter candidates down to emission-line fluxes of 0.5-1 x 10^-16 erg s^-1 cm^-2, across a total area of 0.56 sq. degrees (2.1 x 10^5 comoving Mpc at z=2.23) in these fields. The BzK colours of the emitters suggest that at least 80% of our sample are likely to be H-alpha emitters (HAEs) at z=2.23. This is one of the largest HAE samples known at z>2. We find modest (~3-sigma) local over-densities of emitters associated with all the three targets. In the 2QZ cluster field, the emitters show a striking filamentary structure connecting four of the z=2.23 QSOs extending over 30Mpc (comoving). In the HzRG and SMG/OFRG fields, the structures appear to be smaller and seen only in the vicinities of the targets. The K-band magnitudes and the H-alpha equivalent widths of the emitters are weakly correlated with the over-density of the emitters: emitters in over-dense region are more evolved systems compared to those in under-dense regions at z=2.23. We find several examples of extended HAEs in our target fields, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z=2.23) in the 2QZ field, suggesting that these are relatively common in high-density regions. We conclude that narrow-band H-alpha surveys are efficient routes to map over-dense regions at high-z and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures.

title: CHARACTERIZATION OF THE DISTRIBUTION OF THE Lyα EMITTERS IN THE 53W002 FIELD AT z = 2.4*
abstract: We present the results of our wide-field narrowband imaging of the field around the radio galaxy 53W002 at z = 2.390 with Subaru/Suprime-Cam. A custom-made filter, NB413, centered at 4140 A with a width of 83 A is used to observe the 31' × 24' area around the radio galaxy. We detected 204 Lyα emitters (LAEs) at z = 2.4 with a rest-frame equivalent width larger than 25 A to the depth of 26 AB mag (in NB413). The entire LAE population in the 53W002 field has an average number density and distributions of equivalent width and size that are similar to those of other fields at z ~ 2. We identify a significant high-density region (53W002F-HDR) that spreads over ≈5' × 4' near 53W002, where the LAE number density is nearly four times as large as the average of the entire field. Using the probability distribution function of density fluctuation, we evaluate the rareness probability of 53W002F-HDR to be 0.9+2.4 – 0.62%, which corresponds to a moderately rich structure. No notable environmental dependency at the comoving scale of 10 Mpc is found for the distributions of the Lyα equivalent width and luminosity in the field. We also detected four Lyα blobs, one of which is newly discovered. They are all located in the rims of high-density regions. The biased location and unique morphologies in Lyα suggest that galaxy interaction plays a key role in their formation.