Sunday, March 24, 2019

calculus - Are there other cases similar to Herglotz's integral int10fraclnleft(1+t4+sqrt15right)1+tmathrmdt?



This post of Boris Bukh mentions amazing Gustav Herglotz's integral
10ln(1+t4+A15)1+t dt=π212(152)+ln2ln(3+5)+ln1+52ln(2+3).

I wonder if there are other irrational real algebraic exponents α such that the integral
10ln(1+tα)1+tdt
has a closed-form representation? Is there a general formula giving results for such cases?



Are there such algebraic α of degree >2 ?


Answer



Here is a list of some of these integrals:

10log(1+t2+3)1+tdt=π212(13)+log2log(1+3)10log(1+t3+8)1+tdt=π224(332)+12log2log(2(3+8)3/2)10log(1+t4+15)1+tdt=π212(215)+log(1+52)log(2+3)++log2log(3+5)10log(1+t5+24)1+tdt=π224(596)+12log(1+2)log(2+3)++12log2log(2(5+24)3/2)10log(1+t6+35)1+tdt=π212(335)+log(1+52)log(8+37)++log2log(5+7)10log(1+t8+63)1+tdt=π212(463)+log(5+212)log(2+3)++log2log(3+7)10log(1+t11+120)1+tdt=π224(11480)+12log(1+2)log(4+15)++12log(2+3)log(3+10)++12log(1+52)log(5+24)++12log2log(2(11+120)3/2)10log(1+t12+143)1+tdt=π212(6143)+log(3+132)log(10+311)++log2log(11+13)10log(1+t13+168)1+tdt=π224(13672)+12log(1+2)log(5+212)++14log(2+3)log(15+224)++14log(5+24)log(8+63)++12log2log(2(13+168)3/2)10log(1+t14+195)1+tdt=π212(7195)+log(1+52)log(25+439)++log(3+132)log(4+15)++log2log(15+13)


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