Query_string not working as expected for multiple fields with AND as default_operator

We are not able to get match for a query on multiple fields using query_string. We are not sure why it is not working even if it's a simple query. Below is the query, document and mapping (index) that we are using:
Query:
{​
"query": {​
"query_string": {
​ "query": "Paliperidone palmitate for cochrane nussbaum",
"default_operator": "AND",
"type": "most_fields",
"fields": ["title", "authors","body"]
}
}
}​
Document:
{
"title" : "Paliperidone palmitate for schizophrenia.",
"body" : "Paliperidone palmitate, long-acting, intramuscular formulation paliperidone, is now available clinical use. Paliperidone is active metabolite risperidone is also available oral formulation daily use.. compare effects paliperidone palmitate any other treatment people schizophrenia schizophrenia-like illnesses.. We searched Cochrane Schizophrenia Group's Register (November 2009) inspected references identified studies further trials.",
"authors" : [
"Abraham M Nussbaum",
"T S Stroup"
]
}
Mappings:
{
"settings": {
"analysis": {
"filter": {
"english_stop": {
"type": "stop",
"stopwords": "english"
},
"test_keyword_marker_filter": {
"type": "keyword_marker",
"keywords_pattern": "NLM*",
"ignore_case": true
},
"lowercase_filter": {
"type": "lowercase"
}
},
"analyzer": {
"test_standard_analyzer": {
"tokenizer": "standard",
"filter": [
"english_stop",
"test_keyword_marker_filter",
"lowercase_filter"
]
}
}
}
},
"mappings": {
"properties": {
"authors": {
"type": "text",
"fields": {
"keyword": {
"type": "keyword",
"ignore_above": 256
}
},
"analyzer": "test_standard_analyzer"
},
"body": {
"type": "text",
"fields": {
"keyword": {
"type": "keyword",
"ignore_above": 256
}
},
"analyzer": "test_standard_analyzer"
},
"title": {
"type": "text",
"fields": {
"keyword": {
"type": "keyword",
"ignore_above": 256
}
},
"analyzer": "test_standard_analyzer"
}
}
}
}