findByPublic.js

var a = 
  { "author" : "Author"
  , "state" : "Published"
  , "section" : "5158bfc0e5aa20eb5c000001"
  , "preTitleHtml" : "<p>PreTitleHtml</p>"
  , "longTitle" : "LongTitle"
  , "shortTitle" : "ShortTitle"
  , "subTitle" : "subTitle"
  , "slug" : "articlea"
  , "standfirst" : "standFirst"
  , "body" : [ ]
  , "images" : [ ]
  , "crops" : { }
  , "pageTitle" : "PageTitle"
  , "pageDescription" : "PageDescription"
  , "seoKeywords" : "SeoKeywords"
  , "social" : [ ]
  , "relatedSections" : [ ]
  , "liveDate" : ISODate("2012-02-01T00:00:00Z")
  , "expiryDate" : ISODate("2015-02-01T00:00:00Z")
  , "dateCreated" : ISODate("2013-03-31T22:59:12.543Z")
  , "displayDate" : ISODate("2012-02-01T00:00:00Z")
  , "archiveDate" : ISODate("2013-10-01T22:59:13.208Z")
  , "showDisplayDate" : true
  , "tags" : [ ]
  , "comments" : true
  , "likable" : true
  , "type" : "article"
  , "subType" : null
  , "_textIndex" : [ "longtitl", "shorttitl" ]
  , "_id" : ObjectId("5158bfc1e5aa20eb5c000004") }
db.article.find(
  {"section":"5158bfc0e5aa20eb5c000001"
  , "slug":"articlea"
  , "state":"Published"
  , "$and":
    [
      {"$or":
        [
          { "liveDate":null}
          , { "liveDate": {"$lte":"2013-03-31T22:59:13.229Z"}}
        ]}
      ,{"$or":
        [{"expiryDate":null},{"expiryDate":{"$gte":"2013-03-31T22:59:13.229Z"}}
        ]}
    ]
  })

The string dates would actually be proper dates when via the driver