[Paper Review] Experimental Signatures of Kahler Stabilization of the Dilaton

Brent Nelson|ArXiv.org|Jul 20, 2003

Geophysics and Sensor Technology3 citations

TL;DR

This paper proposes that Kähler stabilization of the dilaton in heterotic string-based models leads to a vanishing vacuum energy and suppressed soft supersymmetry-breaking terms, resulting in a distinctive collider phenomenology with light gluinos and non-universal gaugino masses. The key result is that such models yield detectable signatures—particularly same-sign dileptons and multi-jet events—at the Tevatron, offering stronger experimental prospects than conventional mSUGRA scenarios.

ABSTRACT

We investigate the collider signatures of modular invariant gaugino condensation, with Kahler stabilization of the dilaton, in the context of weakly coupled heterotic string-based models as an example of how supergravity can be used to build a meaningful string phenomenology.

Motivation & Objective

• To explore how Kähler stabilization of the dilaton in heterotic string models leads to a finite, stabilized vacuum with vanishing cosmological constant.
• To investigate the resulting soft supersymmetry-breaking terms and their phenomenological implications in the context of supergravity effective field theories.
• To identify distinctive collider signatures—especially in gaugino masses and R-parity violating channels—that distinguish Kähler-stabilized models from conventional mSUGRA.
• To demonstrate that these models offer significantly improved prospects for experimental detection at the Tevatron due to lighter gluino masses and enhanced event rates in specific signatures.

Proposed method

• Uses a supergravity framework with a nonperturbative correction to the dilaton Kähler potential, modifying $K_{s\bar{s}}$ from its tree-level form.
• Imposes the condition $\langle V\rangle = 0$ to derive a constraint on the effective parameter $a_{\rm np} = \sqrt{K_{s\bar{s}}^{\rm tree}/K_{s\bar{s}}^{\rm true}}$, which measures departure from tree-level Kähler potential.
• Assumes gaugino condensation in the hidden sector as the source of the dilaton superpotential, with $W(S) \propto e^{-3S/(2b_+)}$, where $b_+$ is the beta-function coefficient.
• Derives one-loop soft terms using the supergravity formulae, including anomaly-mediated contributions that are not suppressed by $a_{\rm np}$, leading to non-universal gaugino masses.
• Performs benchmark scans for $b_+ = 0.095, 0.057, 0.228$, corresponding to $SU(5)$, $SU(3)$, and $E_6$ hidden sector condensates, respectively.
• Simulates collider signatures using PYTHIA at the generator level, estimating event counts for 2 fb⁻¹ luminosity without detector-level cuts, focusing on missing energy and lepton/jet final states.

Experimental results

Research questions

• RQ1 How does Kähler stabilization of the dilaton affect the soft supersymmetry-breaking spectrum in string-inspired models?
• RQ2 What are the collider signatures of a stabilized dilaton with vanishing vacuum energy and suppressed $F^S$-mediated soft terms?
• RQ3 Can models with Kähler-stabilized dilatons produce detectable event rates at the Tevatron despite light gluino masses?
• RQ4 How do loop corrections from the conformal anomaly alter the universality of gaugino masses in this framework?
• RQ5 What is the impact of varying the hidden sector gauge group ($SU(5)$, $SU(3)$, $E_6$) on the resulting phenomenology and detectability?

Key findings

• Kähler stabilization leads to a suppressed $F^S$-contribution to soft terms, with $a_{\rm np} \ll 1$, resulting in $|F^S/M| \ll 1$ and significant non-universalities in gaugino masses.
• The gluino mass is substantially lighter than in mSUGRA—around 330–470 GeV—due to the suppression of tree-level contributions and non-universal loop corrections.
• The LSP is a mixed bino–wino state (89–99% bino), avoiding the pure bino or pure wino character seen in anomaly mediation, enabling viable neutralino relic density.
• The same-sign dilepton channel shows particularly low backgrounds and could yield a few dozen detectable events, making it a promising discovery channel.
• The model with $b_+ \approx 0.095$ ($SU(5)$) yields ~100 multi-jet events and ~30 same-sign dilepton events in 2 fb⁻¹, exceeding mSUGRA in detectability.
• The focus point effect is evident in small $\mu$-terms (245–631 GeV) despite large scalar masses, due to the suppression of $F^S$-mediated contributions.