KATRIN sensitivity to sterile neutrino mass in the shadow of lightest neutrino mass

The presence of light sterile neutrinos would strongly modify the energy spectrum of the tritium beta electrons. We perform an analysis of the KArlsruhe TRItium Neutrino (KATRIN) experiment's sensitivity by scanning almost all the allowed region of neutrino mass-squared difference and mixing angles of the 3 + 1 scenario. We consider the effect of the unknown absolute mass scale of active neutrinos on the sensitivity of KATRIN to the sterile neutrino mass. We show that after 3 years of data-taking, the KATRIN experiment can be sensitive to mixing angles as small as sin(2)2 theta(s) similar to 10(-2). Particularly we show that for small mixing angles, sin(2)2 theta(s) less than or similar to 0.1, the KATRIN experiment can give the strongest limit on active-sterile mass-squared difference.