Excel Services and PowerPivot for SharePoint

http://blogs.technet.com/b/excel_services__powerpivot_for_sharepoint_support_blog/archive/2013/11/06/excel-services-2010-amp-2013-kerberos-configuration.aspx

Claims to Windows Token Service (C2WTS)

http://msdn.microsoft.com/en-us/library/hh231678%28v=sql.110%29.aspx

Troubleshooting Kerberos in Excel Services and PowerPivot for SharePoint

http://blogs.technet.com/b/excel_services__powerpivot_for_sharepoint_support_blog/archive/2013/02/08/troubleshooting-kerberos-for-excel-services-and-powerpivot.aspx

Install PowerPivot for SharePoint

http://msdn.microsoft.com/en-us/library/ee210708%28v=sql.110%29.aspx

Deployment Checklist: Reporting Services, Power View, and PowerPivot for SharePoint

http://msdn.microsoft.com/en-us/library/hh231687%28v=sql.110%29.aspx