[Paper Review] D-term assisted Anomaly Mediation in E6 motivated models

Masaki Asano, T. Kikuchi+1 more|ArXiv.org|Jul 31, 2008

Particle physics theoretical and experimental studies39 references4 citations

TL;DR

This paper proposes a D-term assisted anomaly mediation scenario in E6-motivated GUT models, where an additional U(1)S D-term from E6 unification stabilizes slepton masses against tachyonic behavior. By introducing this D-term, the model generates distinct sparticle mass spectra with left-right sfermion mass splittings, offering unique LHC signatures. The model achieves a WMAP-consistent dark matter relic density, potentially allowing light neutralino dark matter via non-thermal production.

ABSTRACT

We investigate effects of D-term contributions to the anomaly mediated supersymmetry breaking scenario. If we introduce an E6 GUT motivated D-term, it is possible that slepton mass squared is positive at weak scale even if there are no other D-term contributions. Moreover, as a consequence of additional D-term contributions to scalar masses, we obtain various soft supersymmetry breaking mass spectra, which are different from those obtained in the conventional anomaly mediation scenario. Then there would be a distinct signature of this scenario at the LHC. For example, in several cases, there exist mass splittings between the right-handed sfermion and the left-handed sfermion. We also discuss some characteristic features of the neutralino dark matter in this model.

Motivation & Objective

• To resolve the tachyonic slepton problem in conventional anomaly-mediated SUSY breaking (AMSB) by introducing additional D-term contributions.
• To explore the phenomenological implications of a U(1)S D-term arising from E6 GUT symmetry, beyond standard U(1)Y and U(1)B-L terms.
• To investigate how this new D-term modifies soft SUSY breaking mass spectra and leads to observable signatures at the LHC.
• To evaluate the relic density of the lightest neutralino as a dark matter candidate and assess its consistency with WMAP data.
• To determine whether light neutralino dark matter can be viable in this scenario, especially via non-thermal production mechanisms.

Proposed method

• The model introduces a U(1)S gauge symmetry from E6 GUT, with its D-term contribution to scalar masses calculated via the Fayet-Iliopoulos mechanism.
• Soft SUSY breaking masses are computed using a modified anomaly mediation framework, including D-term contributions from U(1)Y, U(1)B-L, and U(1)S symmetries.
• The scalar mass squared terms are derived from the sum of anomaly-mediated contributions and D-term contributions, with D-terms parameterized by αY, αB-L, and αS.
• Spallate mass spectra are numerically computed using ISAJET 7.75, with focus on sfermion mass splittings and chiral structure.
• Dark matter relic density is evaluated using micrOMEGAs, considering both thermal and non-thermal production mechanisms.
• Parameter spaces for (DY, DB-L, DS) are scanned to identify regions consistent with WMAP constraints on ΩCDMh².

Experimental results

Research questions

• RQ1 Can a U(1)S D-term from E6 GUT stabilize tachyonic slepton masses without requiring additional U(1)Y or U(1)B-L D-terms?
• RQ2 How do D-term contributions from U(1)S modify the soft SUSY breaking mass spectrum, particularly the left-right sfermion mass splitting?
• RQ3 What are the distinctive LHC signatures arising from these modified mass spectra, especially in squark and slepton decays?
• RQ4 Is the lightest neutralino a viable dark matter candidate in this model, and can it achieve the observed relic density?
• RQ5 Can light neutralino dark matter be consistent with WMAP data if non-thermal production is considered?

Key findings

• The inclusion of a U(1)S D-term alone is sufficient to stabilize tachyonic slepton masses, solving the tachyonic problem in a more economical way than requiring U(1)Y and U(1)B-L D-terms.
• The model generates significant mass splittings between left-handed and right-handed sfermions, leading to distinctive decay patterns such as jet or lepton multiplicity in right-handed squark decays.
• The relic density of the lightest neutralino is consistent with WMAP data only when the neutralino is heavy (M_SUSY ≈ 5 TeV) in the thermal scenario, due to rapid Wino-like annihilation.
• Non-thermal production of the LSP neutralino from moduli decays allows for a viable light neutralino dark matter candidate, even with low M_SUSY.
• The model predicts a distinct signature at the LHC due to chiral mass splittings, particularly in the sfermion sector, enabling potential discrimination from conventional AMSB.
• The parameter space (αY, αB-L, αS) allows for viable solutions with WMAP-consistent dark matter, especially when non-thermal production is included.