Q: How should I mention the author affiliation when I have retired from work?

If the institution you are last affiliated to had paid for your research or if you had conducted most of the research at the time you were employed, you should still use the affiliation of your previous institution. However, if the majority of the work was done after your retirement, you can use the term "Independent Researcher." Another option is to just add "Retired" after your previous affiliation and continue publishing.

However, there is a third option which would be really beneficial for you if you are interested in continuing research after your retirement. Many universities offer a Professor Emeritus status where retired professors have certain rights, such as a small office at the university department they worked at and access to the library and laboratory. In return, you might be asked to take a few classes or review some papers. Talk to other professors of your department and see if you can initiate this system in your university. Other professors would, I'm sure, agree to it since they would also get the same benefits after retirement. 

You might also find the following post useful:

• What should be the affiliation of an institution's ex-employee in research publications?
• Can a retiree include his or her former organization as an affiliation on a manuscript?