Sparticle Spectra and LHC Signatures for Large Volume String Compactifications

TL;DR

This study links large-volume string compactifications with an intermediate string scale to TeV-scale supersymmetry and LHC phenomenology by computing soft terms including magnetic flux perturbations, running RGEs to the weak scale, and generating random spectra. It finds a characteristic gaugino pattern $M_1:M_2:M_3\approx(1.5$–$2):2:6$ and a relatively compressed scalar sector, distinguishing these models from mSUGRA and mirage mediation. Through Monte Carlo collider studies, counting observables, and endpoint-based mass reconstruction, the work demonstrates that 100 fb$^{-1}$ of LHC data can discriminate large-volume models and recover key sparticle mass differences, despite uncertainties from flux perturbations. This work provides a concrete framework to test string-inspired SUSY scenarios at colliders and highlights robust observables for model discrimination and spectrum reconstruction.

Abstract

We study the supersymmetric particle spectra and LHC collider observables for the large-volume string models with a fundamental scale of 10^{11} GeV that arise in moduli-fixed string compactifications with branes and fluxes. The presence of magnetic fluxes on the brane world volume, required for chirality, perturb the soft terms away from those previously computed in the dilute-flux limit. We use the difference in high-scale gauge couplings to estimate the magnitude of this perturbation and study the potential effects of the magnetic fluxes by generating many random spectra with the soft terms perturbed around the dilute flux limit. Even with a 40% variation in the high-scale soft terms the low-energy spectra take a clear and predictive form. The resulting spectra are broadly similar to those arising on the SPS1a slope, but more degenerate. In their minimal version the models predict the ratios of gaugino masses to be M_1 : M_2 : M_3=(1.5 - 2) : 2 : 6, different to both mSUGRA and mirage mediation. Among the scalars, the squarks tend to be lighter and the sleptons heavier than for comparable mSUGRA models. We generate 10 fb^{-1} of sample LHC data for the random spectra in order to study the range of collider phenomenology that can occur. We perform a detailed mass reconstruction on one example large-volume string model spectrum. 100 fb^{-1} of integrated luminosity is sufficient to discriminate the model from mSUGRA and aspects of the sparticle spectrum can be accurately reconstructed.

Figures (9)

• Figure 1: ${\not\!\!p_T}$ plot for background and a sample signal spectrum. The background is shown in red. The spike in the background ${\not\!\!p_T}$ at 200 GeV is an artifact of the triggers used.
• Figure 2: Comparison of results with $20\%$ and $40\%$ variations: di- and tri-leptons counts and events with $b$-jets.
• Figure 3: Comparison of event numbers with $20\%$ variations and varying mass scale, and results for the SPS1a slope: (a) numbers of tri-leptons/OS di-leptons, (b) number of events with 2 leptons, 1 or 2 $b$-jets and 2 jets/number of events with 2 leptons, 0 $b$-jets and 2 jets.
• Figure 4: Opposite sign, same flavour di-lepton invariant mass for (a) a spectrum with many di-lepton events and $m_{\tilde{\chi}_2}\gg m_{\tilde{\chi}_1}$ and (b) a spectrum with few di-lepton events and $m_{\tilde{\chi}_2^0}-m_{\tilde{\chi}_1^0}\approx 21$ GeV. In both cases we require 4 hard jets and ${\not\!\!p_T} \ge 200$ GeV. Standard Model background is shown in red.
• Figure 5: $M_{ll}$ after cuts selection A. We expect an edge at $\sim 69$ GeV from the spectrum. The Standard Model background is shown in red.