55904501
MadGolem: automated NLO predictions for Beyond-the-Standard Model searches
TeV-scale new physics is already at the spotlight of the current experimental LHC program. In this context, particle phenomenologists are urged to develop automated tools aiming at fast, flexible and accurate theoretical predictions for the major new physics discovery channels. In this contribution we provide a summarized description of the MADGOLEM package, a fully automated tool that enables to evaluate next-to-leading order (NLO) cross sections and distributions for generic heavy particle pair production beyond the Standard Model (BSM). We concisely portray the structure and inner architecture of the code, with our main emphasis on the strategies by which we handle the genuine building blocks of a NLO calculation ‐ the evaluation of the one-loop amplitudes, the renormalization of the ultraviolet singularities, and the subtraction of infrared and on-shell divergences. We discuss the performance of the tool, its multiple functionalities and analysis options, and the attentive cross-checks of all these features. Finally, we present some sample applications to BSM heavy particle production at the LHC.
17463150
T-odd asymmetries in radiative top-quark decays
We study the angular distribution of the charged lepton in the top-quark decay into a bottom quark and a W boson which subsequently decays into lνl, when a hard gluon is radiated off. The absorptive part of the t → bWg decay amplitudes, which gives rise to T-odd asymmetries in the distribution, is calculated at the one-loop level in perturbative QCD. The asymmetries at a few percent level are predicted, which may be observable at future colliders.
119273887
HELAS and MadGraph with spin-3/2 particles
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.
118592790
Collider signatures of goldstini in gauge mediation
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.
118501818
Simulating spin-$\frac{3}{2}$ particles at colliders
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.
18591095
TauDecay: a library to simulate polarized tau decays via FeynRules and MadGraph5
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.
119225495
CHARACTERIZATION OF THE DISTRIBUTION OF THE Lyα EMITTERS IN THE 53W002 FIELD AT z = 2.4*
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.