\documentclass[tikz]{standalone}
\usetikzlibrary{calc}
\begin{document}


\pgfmathsetmacro{\xmax}{7}
\pgfmathsetmacro{\ymax}{\xmax}

\begin{tikzpicture}[scale=0.6]
% coordinates
\coordinate (O)  at  (0,0);
\coordinate (L)  at  (\xmax, {\xmax * 0.4});
\coordinate (H)  at  (\xmax, {\xmax * 0.51/0.6});
\coordinate (T1) at  ($(O)!0.45!(L)$);
\coordinate (T2) at  ($(O)!0.75!(H)$);

% axes
\draw[->] (0,0) -- (\xmax,0)
  node[right=2pt] {$q$};
\draw[->] (0,0) -- (0,\ymax)
  node[above=2pt] {$p$};

\draw[] (0,0) -- (L)
  node[right=2pt] {$\theta_L$};
\draw[] (0,0) -- (H)
  node[right=2pt] {$\theta_H$};

% Lower curve
% Tangency point at (T1)
\draw[lightgray, ultra thick]
  (T1)
    to [bend left=6]
  ++(-1.8,-0.3);
\draw[lightgray, ultra thick]
  (T1)
    to [bend right=6]
  ++(1.8,1.3);

% Upper curve
% Tangency point at (T2)
\draw[lightgray, ultra thick]
  (T2)
    to [bend left=8.1]
  ++(-1.8,-0.8);
\draw[lightgray, ultra thick]
  (T2)
    to[bend right=8.1]
  ++(1.2,1.8);

% Tangency points
\fill (T1) circle (2.7pt);
\fill (T2) circle (2.7pt);

\draw[dotted]
  (T1 |- O)
    node[below=2pt] {$q_L^{\mathrm{FB}}$} --
  (T1) -- (O |- T1)
    node[left=2pt] {$p_L^{\mathrm{FB}}$};

\draw[dotted]
  (T2 |- O)
    node[below=2pt] {$q_H^{\mathrm{FB}}$} --
  (T2)  -- (O |- T2)
    node[left=2pt] {$p_H^{\mathrm{FB}}$};

\end{tikzpicture}
\end{document}