# Questions tagged [notation]

This tag is for questions on the meaning, history, and usage of various symbols and notation that are used to denote different quantities in physics. Don't forget to mention the reference, where you encountered those notations.

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### Expectation Value of Operator [closed]

In the book Modern Quantum Mechanics by Sakurai the expectation value of A is defined as $$\left <A\right> = \left<\psi\right|A\left|\psi\right>$$ And, we can also write it as (as ...
1 vote
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### Confusion about left/right-handed spinor notations

Peskin & Schroeder eq (3.78) states that $$(\bar{u}_{1R}\sigma^\mu u_{2R})(\bar{u}_{3R}\sigma_\mu u_{4R})=\cdots$$ But I don't understand what the $u_{1R}$ means. Since 4-component Dirac spinor ...
275 views

### What is this vector notation? For linear retardance calculation

Consider: I found this formula in https://doi.org/10.1364/BOE.426653 (NLM), a paper titled: Stokes polarization imaging applied for monitoring dynamic tissue optical clearing. The formula is for ...
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### Notation Clarification of $G_{\uparrow\uparrow}$

I am a bit confused as to what the notation $$G_{\uparrow\uparrow}$$ on the Green fucntions means, on a paper I have come across. Here $\hat{G}(k) = (i \omega_{l} - H_{I} - H_{P})^{-1}$. The ...
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1 vote
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### How does a vector field transform in quantum mechanics?

( I understand my question is a bit vague. I will try to make it more precise at the end ). Consider a vector field $\Phi^i$ in quantum mechanics. The crux of my question is, how does it transform? In ...
1 vote
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### Difference between $\mathcal{N}=2$ and $\mathcal{N}=(1,1)$ SUSY

In supersymmetry algebra, $\mathcal{N}$ refers to $I=1,2,.. \mathcal{N}$ in $Q^{I}_{\alpha}$. My question is what does it mean to write $\mathcal{N}=(1,1)$ superalgebra?
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### Square notation for Lagrangian terms

I am starting field theory and have questions regarding what I learned about tensor/Einstein notation. I made up my own problem where I am deriving things backwards to practice tensor notation and ...