the Efficiency Hypothesis
I doubt that's a good choice of phrase for a PhD title, regardless of capitalization. "efficiency" comes up everywhere. This is super-vague. At least somethin like "Smith's Efficiency Hypothesis" or "The [process name] fficiencyefficiency Hypothesis" if that's the process you want to make efficient. Remember, the PhD title will be read not just by people in your specific subfield, but by people with very diverse backgrounds.