What action to take when questions regarding a published paper are ignored by its author? Recently, our group is trying to reproduce the result reported by a paper whose authors are from an Ivy league university. We are unable to reproduce the results because there are several implementation details are not mentioned in the paper. Hence, we decide to write the first author, who is now already a faculty member in another university, an email.

At first, we asked for the code, which we consider is perfectly fine, as the paper has been published. We feel the code in a published paper is no longer a secret in this transparent research era where reproducibility is highly valued. However, he simply ignored our email (3+ weeks, no response).

Then, we thought, OK, seems that he is reluctant to share the code, so let's just ask him to clarify several implementation details so that we can implement the thing ourselves and hopefully, we can reproduce the result. So, we sent a second email which very clearly asks for clarifications. Again, he ignored the email (1.5 weeks+, no response).

We now feel angry and start suspecting the authenticity of their reported results. However, we cannot accuse them of anything, since we are not able to prove that they cheated, which would be a felony if they really did.

We always feel that upon the publication of a paper, its authors, or at least the correspondence author, hold responsible for any inquiries regarding the paper, especially when the authenticity is being doubted. What they chose to do - ignoring our email - is really irresponsible.

What can we do?

Disclaimer

Thanks for the answers and comments! It is interesting that many start besieging me on my "bad" attitude in the email. 

Just to clarify, 


I wrote perfectly polite emails to the correspondence author;
I have NOT questioned his results or whatsoever.
How do you know he ignored the email?

Maybe he never received it because it was filtered before he had a chance to see it. Maybe he hasn't read his email this month because he's on vacation. Maybe that email address was good when the paper is published but not good now, but it's also not bouncing. 

If one channel of communication doesn't work, try a different one. Call his office phone or send a letter to him. Write to a different author saying you've been trying to reach the corresponding author without success and you want to check the email address. Don't assume anything when you have no information.