Hi @g.mitsu2011 welcome to the forum.
Let's start first with a couple of things that will make your life easier. First thing you need to do is to update Arnold. As you can see here you are using an older version.

Second thing is that Arnold has its own render view, and you can find it here

Then you don't need this exposure control

Use the no exposure control and then in the Arnold Render View add an Exposure and tonemapping imager.
Last point, for the scene you have, these settings are a little bit too high, which will make the render slow

Something like Camera AA 4, Diffuse 3 3, Specular 3 2 should be enough. Just a brief explanation, but the Camera AA works a global multiplier for the values bellow, and usually you need to increase it when you have Depth of Field or Motion blur.
Last to answer you question. Use an Arnold Skydome light to create that white background.

Create the light, select the option Light Shape Visible and color by default is white.
If you need more help, feel free to ask. You can also check the youtube channel
https://www.youtube.com/c/arnoldrenderer
There is also an non official Arnold discord server
https://discord.gg/YjmVSsT
And don't forget to check the User Guide
https://docs.arnoldrenderer.com/display/A5AF3DSUG