Just addressing general principles here, and not your specific case:
Defamation of character is a tort. That means a personal injury action. From my own practice, these claims have short windows of opportunity, typical statutes of limitation are one year or less. So, first things first, if you are seriously contemplating pursuing such an action, consult with an attorney so that you can plan to file your claim in a timely fashion.
Certain lies about another are considered so boldly evil or bad that a person victimized by such accusations, if false, does not even have to prove that they actually suffered any compensable injury. Instead, the law will allow a jury to presume that, if these kind of accusations were falsely made, injury occurred. Among allegations that, if false, create a presumption of injury are the charge that a licensed professional (doctor, lawyer, dentist) was incompetent in their profession, another is the allegation of certain crimes falsely alleged (murder, for example), another is the unfounded allegation of homosexuality.
The allegation that you harassed another, at this level of detail, doesn't seem to fall within the category of defamations within which you are not required to prove actual injuries. So, in a hypothetical case based on your facts, you would have to prove injury or harm, as well as falsity.
It would be well worth your time to consult with an attorney in your jurisdiction. Do so sooner rather than waiting, as you may have a limited time within which to sue.
This answer is not a substitute for consulting with and retaining the services of an attorney for your legal needs. By providing this answer, I am not entering into an attorney client relationship with you.
The quasi-privilege of "common interest" (CA Civil Code sec 47) will ordinarily operate to defeat defamation actions in circumstances such as yours. Even more critically, the co-worker who made the complaint had a right to make that complaint and your employer then had a legal obligation to investigate it. In all events, it is unlikely that a claim for defamation can be successfully maintained here.
It may be worthwhile for you to consult with a CA worker's comp attorney to consider a claim for the psychic and emotional injuries that you are struggling with.
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I believe that you may have a valid suit against them, but that would depend on what the "false harassment accusations" were and other facts regarding the circumstance. I would speak to a civiil litation attorney for a consultation, to assess the specific facts of the case.
The Statute of Limitations in California for defamation/libel is 1 year. However it may be shorter if the employer is a governmental agency. Defamation/libel suits are very difficult to prove and even though you feel that you have been injured as a result the connection between what they said/wrote and your problems would be very hard to prove. I agree with the other answers. You can certainly consult with an attorney in your area but this does not look promising to me. Best of luck.
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