Math font Helvetica non-italic

No. You don't say anything about how you are configuring Helvetica for text. Probably you are saying something like

usepackage{helvet}

(which isn't actually Helvetica, of course) or

usepackage{tgheros}

or similar. Or you might be using a system font called Helvetica or Helvetica Neue with fontspec.

Whichever method you are using, you cannot use it for maths because it is a text font and not a maths font. For maths, you need fonts using the appropriate maths encodings. You can use certain elements from a text font in maths e.g. for variables and letters. But that does not get you Greek etc. For those you need appropriately encoded maths fonts.

There are one or two sans serif fonts for maths, such as the set used by Beamer. So if sans serif is the point, you may be in luck. But for Helvetica and its many clones themselves, the fonts don't exist.

Take a look at the TeX Font Catalogue's list of fonts with maths support to find something you like.

Fonts which either are sans-serif with maths support or offer one or more options for sans-serif with maths include:

• Arev,
• Computer Modern Bright,
• Fira Sans,
• Iwona (variants available),
• KP (variants available),
• Kurier,
• KP,
• LX

Use:

usepackage{arev}
renewcommand{rmdefault}{phv}
usepackage{mathastext}

See https://gist.github.com/Pni0/2923266 for a means to use helvet for math:

renewcommand{familydefault}{sfdefault}
usepackage[scaled=1]{helvet}
usepackage[helvet]{sfmath}
everymath={sf}

Worked for me.