Different \mathcal{J}

Question

For my book I would like a specific symbol for "J" with a glyphs on the head as shown in the following images:

1. First image:

2. Second image:

Exist, peraphs, a command or a fine macro to obtain a similar shape?

Now I'm using now the packages times from https://ctan.org/pkg/times and mtpro2 v. lite https://ctan.org/pkg/mtp2lite and the classical calligraphic fonts using the command \mathcal{J}.

I would like that the symbol has the same size as the \mathcal{T} with the options normal, the slanted (inclined) and the bold character.

I often use \boldsymbol{...} command and I compile my file .tex only with pdfLaTeX.

Thanks to everybody for your precious help.

Answer 1

If you really want a J with a T head :

• By using adjusbox you can cut out the J bottom and the T head. For example: \def\hJ{\clipbox{0 -0.05ex 0 0.1em}{$J$}} \def\hT{\raisebox{0.45em}{\clipbox{0 0.45em 0 0em}{$T$}}}
• You combine them with the suitable \mkern. Using the mathllap command from mathtools package : $\mathllap{\hT}\mkern-15mu\hJ$ gies the desired symbol (mathtalic)

To get the bold or upright version you will have to adjust the kerning because the width is different. And for boldface you will not be able to use \bm but will return to the old \boldmath put in another box. A compromise would be to pass the kern amount as a parameter :

\newcommand\JJ[1][15]{\hT\mkern -#1mu\hJ}
\newcommand\JJbf{\mbox{\boldmath$\JJ[14.2]$}}

  $\JJ  : \square \mathbf{A} = \mu_0 \,\JJbf$

produces the picture below.

The makeshift (not a real solution) suggested here should work with any font instead of the default latin modern I used in the first picture. If you want to use another (math)font you simply would have to find the correct kerning, which is font dependent. For the other variants (bold, upright etc.), simply add \mathrm or \mathbf or whatever needed in the definitions of \hT and \hJ (inside the \clipbox)
To get the result in the four mathstyles you will have to use \mathchoice, explained in several post on this forum. Here is a full MWE using times and mtpro2 lite, and the result:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}        
\usepackage{newtxtext}
\usepackage[lite,mtphbi]{mtpro2}
\usepackage[scaled=0.92]{helvet}
\usepackage{amsmath,amssymb}        
\usepackage{adjustbox}

\def\hJ{\mathchoice%
{\clipbox{0 -0.05ex 0 0.1ex}{$J$}}%
{\clipbox{0 -0.05ex 0 0.1ex}{$J$}}%
{\clipbox{0 -0.05ex 0 0.1ex}{$\scriptstyle J$}}%
{\clipbox{0 -0.05ex 0 0.1ex}{$\scriptscriptstyle J$}}%
}
\def\hT{\mathchoice%
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$T$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$T$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\scriptstyle T$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\scriptscriptstyle T$}}}
}

\def\hJbf{\mathchoice%
{\clipbox{0 -0.05ex 0 0.1}{$\mathbf{J}$}}%
{\clipbox{0 -0.05ex 0 0.1}{$\mathbf{J}$}}%
{\clipbox{0 -0.05ex 0 0.1}{$\scriptstyle \mathbf{J}$}}%
{\clipbox{0 -0.05ex 0 0.1}{$\scriptscriptstyle \mathbf{J}$}}%
}
\def\hTbf{\mathchoice%
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\mathbf{T}$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\mathbf{T}$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\scriptstyle \mathbf{T}$}}}
{\raisebox{0.45ex}{\clipbox{0 0.45ex 0 0}{$\scriptscriptstyle \mathbf{T}$}}}
}

\newcommand\JJ[1][15.2]{\hT\mkern -#1mu\hJ}
\newcommand\JJbf[1][11.5]{\hTbf\mkern -#1mu\hJbf}

\begin{document}
\huge
A big regular J : $J\quad \mathrm{J}\quad \mathbf{J}$\par
A big regular T : $T\quad \mathrm{T}\quad \mathbf{T}$

This is custom J : $\JJ  \quad  \square \mathbf{A} = \mu_0 \,\JJbf$

$\JJbf_{\JJ_{\JJ}}$
\end{document}

Answer 2

With mathalfa you can select from a large number of fonts. See What are all the font styles I can use in math mode?.

A symbol similar to yours is here.

\documentclass{article}
\usepackage[cal=pxtx]{mathalfa}
\begin{document}
$\mathcal{J}$
\end{document}

If it's not appropriate, check the table in Christian's answer for the aforementioned question.