Latex (Math) highlight is broken when auctex is installed

[milanglacier]

two versions of minimal config (one with auctex installed and one without auctex installed)

the first is without auctex installed:

(require 'package)
(setq package-user-dir "~/Downloads/emacs-package-dir")

(setq package-list '(poly-R poly-markdown ess))
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
(package-initialize)

(unless package-archive-contents
  (package-refresh-contents))

(dolist (package package-list)
  (unless (package-installed-p package)
    (package-install package)))

(setq markdown-enable-math t)
(setq warning-minimum-level :error)

emacs -Q -l minimal-config.el opens the following rmd file: test.rmd

---
title: 'test rmd'
author: 'author'
date: '12/14/2021'
output: 
    bookdown::pdf_document2:
---

$y = \sum_{i=1}^n sin5x^3 + 2$

the rendering is the following:

and if with auctex installed:

(require 'package)
(setq package-user-dir "~/Downloads/emacs-package-dir")

(setq package-list '(poly-R poly-markdown ess))
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
(package-initialize)

(unless package-archive-contents
  (package-refresh-contents))

(dolist (package package-list)
  (unless (package-installed-p package)
    (package-install package)))

(setq markdown-enable-math t)
(setq warning-minimum-level :error)

emacs -Q -l minimal-config.el opens the same file, will see that math (latex) highlight is broken:

It is clear that the highlight of the keyword (\sum) is broken, and the variable pitch for superscript and subscript is also broken