Manifestly Lorentz invariant nature of the equation $\phi(x)=\int\frac{d^3k}{(2\pi)^3\sqrt{2\omega_k}}(a_k e^{-ikx}+a^{\dagger}_ke^{ikx})$
34228
Lorentz Invariant Integration Measure
98800
Do local flows of left-invariant vector fields satisfy $\Phi_X^t\circ L_x=L_x\circ \Phi_X^t$?
100810
Let $V$ be spherically symmetric and $W$ i.i.d. Gaussian. Then $E[V|V+W=t]=g(\|t\|)$
122603
How does $\mathcal E(\rho)=\mathrm{Tr}_{env}[U(\rho\otimes\rho_{env})U^\dagger]$ turn into $P_0\rho P_0+P_1\rho P_1$?
61073
Why is electric flux defined as $\Phi = E \cdot S$?
10109
What quantities are Lorenz-Invariant?
153205
Why is the $(\frac{1}{2},\frac{1}{2})$ representation of the Lorentz group realized as the vector space of Hermitian $2\times 2$ matrices?
29740
What is the physical significance of the imaginary part when plane waves are represented as $e^{i(kx-\omega t)}$?
124863
Performing Wick Rotation to get Euclidean action of a scalar field $\Psi$
122357
Discreteness of Spacetime and Violation of Lorentz symmetry
6843
Explain $\iint \mathrm dx\,\mathrm dy = \iint r \,\mathrm \,d\alpha\,\mathrm dr$
51122
Lagrangian of Schrodinger field
9753
How to solve the equation $\phi(n) = k$?
138883
How to get the fourth component of EOM in a relativistic formulation of a charged particle in an electromagnetic field?
36797
How do I construct the $SU(2)$ representation of the Lorentz Group using $SU(2)\times SU(2)\sim SO(3,1)$ ?
22024
How to prove that orthochronous Lorentz transformations $O^+(1,3)$ form a group?
153819
Why is $p_\phi$ conserved in a Schwarzschild orbit?