Dark photon constraints using the ultrahigh-energy gamma-ray emission from galactic sources. A phenomenological study

Dark photons (Dphs) appear in theories beyond the Standard Model of particles (SM). Under certain conditions, it is possible to have a mixing between SM photons and Dphs that should be observed as anomalies in the spectrum of astrophysical sources. Our aim is to either find evidence of or set constraints on the existence of Dphs with masses in the range of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi mathvariant="normal">μ</a:mi> <a:mi>eV</a:mi> </a:math> using observations of two galactic sources observed at TeV energies. We use the flux of the Crab Nebula and MGRO <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mrow> <d:mi mathvariant="normal">J</d:mi> <d:mn>1908</d:mn> <d:mo>+</d:mo> <d:mn>06</d:mn> </d:mrow> </d:math> at TeV energies reported by High-Altitude Water Cherenkov observatory and Large High Altitude Air Shower Observatory and assuming a model where Dphs can mix with SM photons in the vacuum; we compute the test statistic to search for evidence of Dphs in the form of variations or attenuation in the observed spectrum. We do not find statistically significant evidence of the existence of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi mathvariant="normal">μ</g:mi> <g:mi>eV</g:mi> </g:math> Dphs. Then, we compute the 68% CL and 95% CL exclusion regions for Dphs with masses in the range from <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:msup> <j:mn>10</j:mn> <j:mrow> <j:mo>−</j:mo> <j:mn>8</j:mn> </j:mrow> </j:msup> </j:math> to <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:msup> <l:mn>10</l:mn> <l:mrow> <l:mo>−</l:mo> <l:mn>5</l:mn> </l:mrow> </l:msup> <l:mtext> </l:mtext> <l:mtext> </l:mtext> <l:mi>eV</l:mi> </l:math> and mixing angles with values between 0.01 and 1.0.