Kohnen and Zagier studied two types of cusp forms Formula: see text on Formula: see text defined by binary quadratic forms. They showed the cusp forms Formula: see text have rational even periods, while Formula: see text have rational odd periods. In this paper, we examine analogous cusp forms Formula: see text on Formula: see text for higher levels Formula: see text. Using locally harmonic Maass forms on Formula: see text, we explicitly compute the even (resp. odd) period polynomials of Formula: see text (resp. Formula: see text). Consequently, we establish that the space of cusp forms of weight Formula: see text on Formula: see text has rational structures, attributed to the periods of these cusp forms.
Soyoung Choi (Tue,) studied this question.