Long/short investment strategies

 are implemented by Vanguard in the following funds:
 * Vanguard Market Neutral Fund
 * Vanguard Managed Payout Funds

S&P 500 130/30 strategy Index

 * Whitepaper:Introducing a Framework for 130/30 Indexation
 * Factsheet:The S&P 500 130/30 Strategy Index
 * Index Methodology

Practitioner papers

 * Philips, Christopher B., CFA, and  Kinniry Jr.,Francis M., CFA, Removing the Long-Only Constraint:The Appeal and Challenges of Implementing 130/30 and Other Long-Short Strategies, Vanguard Investment Counseling & Research (2007)
 * Philips, Christopher B., CFA, and  Kinniry Jr.,Francis M., CFA, Market-Neutral Investing: Strategy Overview and Evaluation, Vanguard Investment Counseling & Research (2008)
 * Yates, Tristan Getting Positive Results With Market-Neutral Funds, investopedia