THE EARLY THERMAL HISTORY OF THE UNIVERSE FROM THE END OF INFLATION UNTIL THE LIGHT ELEMENTS ARE PRODUCED AT BIG-BANG NUCLEOSYNTHESIS REMAINS ONE OF THE MOST POORLY UNDERSTOOD PERIODS OF OUR COSMIC HISTORY. WE DO NOT UNDERSTAND HOW INFLATION ENDS AND THE CONNECTION BETWEEN THE PHYSICS THAT DRIVES INFLATION AND THE STANDARD MODEL IS POORLY CONSTRAINED. CONSEQUENTLY THE MECHANISM BY WHICH THEUNIVERSE IS REHEATED FROM ITS SUPER-COOLED POST-INFLATIONARY STATE INTO A THERMALIZED PLASMA IS UNKNOWN. FURTHERMORE THE PRECISE MECHANISM RESPONSIBLE FOR THE MATTER-ANTIMATTER ASYMMETRY AND THE DETAILED PARTICLE ORIGIN OF DARK MATTER ARE AS YET UNKNOWN. HOWEVER IT IS PRECISELY DURING THIS EPOCH THAT ABUNDANT PHENOMENOLOGY FROM FUNDAMENTAL PHYSICS BEYOND THE STANDARD MODEL ISANTICIPATED.THE OBJECTIVE OF THE PROPOSED RESEARCH IS TO ADDRESS THIS GAP IN OUR UNDERSTANDING OF THE HISTORY OF THE UNIVERSE BY EXPLORING THE CONNECTION BETWEEN THE PHYSICS THAT DRIVES THE INFLATIONARY EPOCH AND THE PHYSICS THAT IGNITES THE HOT BIG-BANG. THIS WILL BE ACHIEVED BY TWO DETAILED STUDIES OF THE PHYSICS OF REHEATING. THE FIRST STUDY EXAMINES THE COSMIC HISTORY OF DARK SECTORS AND ADDRESSES THE COSMOLOGICAL QUESTION OF HOW THESE SECTORS ARE POPULATED IN THE EARLY UNIVERSE. THE SECOND STUDY EXAMINES DETAILED PARTICLE PHYSICS MODELS OF REHEATING WHERE THE INFLATION COUPLES TO GAUGE FIELDS.NASA'S STRATEGIC OBJECTIVES IN ASTROPHYSICS ARE TO DISCOVER HOW THE UNIVERSE WORKS AND TO EXPLORE HOW IT BEGAN AND EVOLVED. THE PRIMARY GOAL OF THIS PROPOSAL IS TO ADDRESS THESE QUESTIONS BY DEVELOPING A DEEPER UNDERSTANDING OF THE HISTORY OF THE POST-INFLATIONARY UNIVERSE THROUGH COSMOLOGICAL OBSERVATIONS AND FUNDAMENTAL THEORY. SPECIFICALLY THIS PROPOSAL WILL ADVANCE NASA'S SCIENCE GOAL TO PROBE THE ORIGIN AND DESTINY OF OUR UNIVERSE INCLUDING THE NATURE OF BLACK HOLES DARK ENERGY DARK MATTER AND GRAVITY.