# Tagged Questions

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### Affine connection notation

Can ${g}^{\mu\sigma}{\Gamma}^{\rho}_{\sigma\nu}$ be written as ${\Gamma}^{\mu\rho}_{\nu}$? If so how come this symbol never appears in any GR book?
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### How are the definitions of a coherent state equivalent?

I am trying to understand coherent states. As far as I could find there are three equivalent definitions and in general many sources start from a different one, still I fail to see their equivalence. ...
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### Derivative with respect to a vector is a gradient?

I've encountered in some books (and even completed an exercise from the Goldstein by using it), a strange notation that seems to work exactly like a gradient, I have tried to look for an explanation ...
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### Notation in Quantum Mechanics

When we write equations in QM, in certain places, the wave function is represented as $\psi(x,t)$, which is the wave function in position space, and in some other places, it is written as $\Psi(t)$. ...
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### What is the chemical symbol for Mu-mesic atoms?

Is there a convention for chemical symbols of mu-mesic atoms, at least for ones bound to light atomic nuclei?
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### Understanding vectors in physics: notation

We have the formula for the Lorentz force $$\textbf{F} = q \space(\textbf{E} + \textbf{v} \times \textbf {B})$$ This is a simple formula you learn in high school, but I'm interested to self-study ...
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### What does $|x⟩|0⟩$ actually mean in bra-ket notation?

Consider the following quote from Wikipedia's page on Shor's algorithm: Initialize the registers to $Q^{-1/2} \sum_{x=0}^{Q-1} \left|x\right\rangle \left|0\right\rangle$ where $x$ runs ...
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### What do physicists mean by ${g^{i}}_j$?

Maybe this is an idiot question, but in relativity I see a lot of ${g^{i}}_j$ for a metric tensor $g$. Is this just $$\delta^i_j ~=~ g(dx^i \sharp, \partial_{ x^j})~?$$
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### Historical reason behind using $ν$ instead of $f$ to stand for frequency in the equation $E=hν$?

Normally, we use the letter $f$ to stand for frequency in equations. $$T = 1/f$$ $$v = \lambda f$$ $$Φ +E_k = h f$$ So I'm curious as why the letter $ν$ (nu) is used to represent frequency in the ...
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### Notation: What is $\delta_{mn}$?

In a textbook, I found this relation for eigenvalues of total angular momentum: $$(L^2)_{mn} = \langle l,m \rvert L^2 \lvert l,n\rangle = \hbar^2l(l+1)\delta_{mn}$$ What is the $\delta_{mn}$ refer to?...
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### What exactly is $\hat{\psi}^\dagger(x)$? An operator or a function?

I've recently read Cohen-Tannoudji on quantum mechanics to try to better understand Dirac notation. A homework problem is giving me some trouble though. I'm unsure if I've learned enough yet to ...
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### Notations for statistical / systematic / numeric errors?

I constantly see the notation $$5.143(13)$$ for specifying that a value was measures / calculated to be 5.143 with an estimated error of 0.013. I have come to wonder though, just how commonly ...
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### Notation for anti-symmetric part of a tensor

I know that $A_{[a} B_{b]} = \frac{1}{2!}(A_{a}B_{b} - A_{b}B_{a})$ But how can write $E_{[a} F_{bc]}$ like the above? Can you provide a reference where this notational matter is discussed?
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### How to deal with the notation of a function $f$ vs its value $f(x)$ in Physics?

This doubt is very silly, but anyway, I think it's worth asking. The problem is: when we work with mathematics, in many situations we want to consider sets $A$ and $B$ and functions $f : A \to B$. ...
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### Topological quantum computation : Anyon model

Could someone tell me about Frobenius-Schur indicator and the associated cups and caps notation in context of anyon model. One possible reference could be Parsa Bonderson thesis which is freely ...
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### Should we necessarily express the dimensions of a physical quantity within square brackets? [duplicate]

For example, should we write the dimension of mass, e.g. $\mathrm{kg}$ as $[M]$ or is it enough to write it as $M$?
In chapter 7 of Peskin and Schroeder they define the field strength renormalisation $Z$ for a quantum field to be the residue of the Fourier transform of the correlation function $$\langle \Omega | \... 1answer 84 views ### Possible abuse of notation in statistical mechanics I know that it often occurs that we need to take a derivitive with respect to \beta in statistical mechanics. However, I think it is poor style to use equations with both T and \beta in them ... 2answers 728 views ### Basic question on bra-ket notation Which of the following corresponds to a  \psi(x), a wavefunction written in the position basis:  x| \psi\rangle  or  \langle x| \psi\rangle ? If it is the second expression (which my textbook ... 3answers 3k views ### What is Si-delta doping? [closed] I want to know what the delta means in this case. I know the Si means the element used, by some way to doping. I guess the delta means that using some elements to create holes in semiconductor made ... 1answer 401 views ### spin parity J^P notation In particle physics, when you read J^P, does it mean Spin parity or total angular momentum parity? I know that the letter J is used for TOTAL angular momentum but I think I read somewhere that ... 1answer 226 views ### Einstein Notation for Strain Energy Function I encounter the following formula (for strain energy function) a lot in physics literature:$$ W(\epsilon_{kl}) = \int_0^{\epsilon_{kl}} \sigma_{ij} \textrm{d}\epsilon_{ij} $$where all indices ... 1answer 345 views ### Notation for Standard Model Charges? Does anybody know what these following numbers describing an electron (1, 1, -1) represent in SU(3) \times SU(2) \times U(1)? Or, these numbers that describe an up quark: (3, 1, 2/3)? I'm ... 0answers 183 views ### Group theory notation used in physics (AdS/CFT) This in the context of the AdS/CFT correspondence. I am reading this review on AdS/CFT Aharony et. al. (The MAGOO review) The abstract can be found here Equation (2.50) of the above paper lists the ... 3answers 423 views ### On Einstein notation with multiple indices On Einstein notation with multiple indices: For example, consider the expression:$$a^{ij} b_{ij}.$$Does the notation signify,$$a^{00} b_{00} + a^{01} b_{01} + a^{02} b_{02} + ... $$i.e. you ... 2answers 686 views ### What is the gamma five matrix \gamma_5? This Wikipedia page explains that for each of the four main gamma matrices \gamma^{\mu}, you can find the covariant matrices \gamma_{\mu} with the equation \gamma_{\mu} = \eta_{\mu\nu}\gamma^{\mu}... 2answers 2k views ### Kronecker delta confusion I'm confused about the Kronecker delta. In the context of four-dimensional spacetime, multiplying the metric tensor by its inverse, I've seen (where the upstairs and downstairs indices are the same): ... 2answers 354 views ### In what order should unit symbols appear? I am trying to represent the result of a dimensional analysis calculation and I can't find an official document that lists the order that unit symbols should appear. For example, when I google 5\... 2answers 8k views ### Difference between \Delta, d and \delta I have read the thread regarding 'the difference between the operators between \delta and d', but it does not answer my question. I am confused about the notation for change in Physics. In ... 1answer 520 views ### Some Dirac notation unclarities Q1: Ok so i have come to a point where i know that \Psi(r,t) which we denote only by \Psi can be represented in a Hilbert space by a vector which we denote \left|\Psi\right\rangle. Does this ... 2answers 359 views ### Why distinguish between row and column vectors? Mathematically, a vector is an element of a vector space. Sometimes, it's just an n-tuple (a,b,c). In physics, one often demands that the tuple has certain transformation properties to be called a ... 2answers 275 views ### Vector \vec{z} and its conjugate transpose \overline{\vec{v}^\top} - is it the same as \left|z\right\rangle and \left\langle z \right| Lets say we have a complex vector \vec{z} \!=\!(1\!+\!2i~~2\!+\!3i~~3\!+\!4i)^T. Its scalar product \vec{z}^T\!\! \cdot \vec{z} with itself will be a complex number, but if we conjugate the ... 1answer 82 views ### Scalar top quark (stop) pair production A rather simple question: Starting from an electrically neutral state, pairs of top quarks are produced as top and anti-top, and denoted as t\bar t. Now the production of pairs of scalar top ... 2answers 317 views ### Difference between slanted indices on a tensor In my class, there is no distinction made between,$$ C_{ab}{}^{b} $$and$$ C^{b}{}_{ab}. $$All I know, and read about so far, is the distinction of covariant and contravariant, form/vector, etc. ... 8answers 7k views ### Is there a symbol for “unitless”? I'm making a table where columns are labelled with the property and the units it's measured in: Length (m) |||| Force (N) |||| Safety Factor (unitless) ||| etc... I'd like not to write "unitless" ... 2answers 339 views ### Inner Product Spaces I am trying to reconcile the definition of Inner Product Spaces that I encountered in Mathematics with the one I recently came across in Physics. In particular, if (,) denotes an inner product in ... 1answer 202 views ### Vector Addition — Direction Say we have three forces F_1, F_2, F_3, such that$$ F_1 + F_2 - F_3 = 0\hspace 10mm (1)  And let us say that $F_1$ and $F_2$ have the same direction and magnitude, and that $F_3$ has double the ...
With the definition of the tensor: $$J_{ij} = I_{ij} - \tfrac{1}{3}\delta_{ij}I^{k}_{k}, \qquad i,j,k\in\{1,2,3\},$$ I have seen the quantity: J_{ij}J_{...