In mathematics and physics, a scalar field or scalar-valued function associates a scalar value to every point in a space – possibly physical space. The scalar may either be a (dimensionless) mathematical number or a physical quantity. In a physical context, scalar fields are required to be independent of the choice of reference frame, meaning that any two observers using the same units will agree on the value of the scalar field at the same absolute point in space (or spacetime) regardless of their respective points of origin. Examples used in physics include the temperature distribution throughout space, the pressure distribution in a fluid, and spin-zero quantum fields, such as the Higgs field. These fields are the subject of scalar field theory.
Homework Statement
(a) Find the christoffel symbols (Done).
(b) Show that ##\phi## is a solution and find the relation between A and B.[/B]
Homework EquationsThe Attempt at a Solution
Part(b)
\nabla_\mu \nabla^\mu \phi = 0
I suppose for a scalar field, this is simply the normal derivative...
Homework Statement
Homework EquationsThe Attempt at a Solution
I solved #2,4 but I don't understand what #1,3 need to me. I know that scalar field is a function of points associating scalar value. But how can I prove some function is scalar field or vector field?
Hi,
I am trying to calculate the laplacian of a scalar field but I might actually need something else. So basically I am applying reaction diffusion on a 2d image. I am reading the neighbours, multiplying them with these weights and then add them.
This works great. I don't know if what I am...
Homework Statement
[/B]
Consider a real free scalar field Φ with mass m. Evaluate the following time-ordered product of field operators using Wick's theorem: ∫d^4x <0| T(Φ(x1)Φ(x2)Φ(x3)Φ(x4)(Φ(x))^4) |0>
(T denotes time ordering)
Homework Equations
Wick's theorem: T((Φ(x1)...Φ(xn)) = ...
Homework Statement
Consider the following real scalar field in two dimensions:
S = \int d^2 x ( \frac{1}{2} \partial_\mu \phi \partial^\mu \phi - \frac{1}{2} m^2 \phi^2 - g \phi^3)
What are the Feynman rules for calculating < \Omega | T(\phi_1 ... \phi_n ) | \Omega >
2. Homework...
Homework Statement
Demonstrate the equivalence between the gauge fields A1=(0,bx,0) and A2=)-yB/2,xB/2,0) and find the scalar field Φ for which A1= A2 + ∇ΦHomework Equations
B = ∇XA
The Attempt at a Solution
The first part is fine, you just plug it into the above relevant equation and you get...
Homework Statement
My question is just about a small mathematical detail, but I'll give some context anyways.
(From Rubakov Sec. 2.2)
An expression for energy is given by
E= \int{}d^3x\frac{\delta{}L}{\delta{}\dot{\phi}(\vec{x})}\dot{\phi}(\vec{x}) - L,
where L is the Lagrangian...
Hi,
f(X)=\frac{xy^2}{x^2+y^4} is the function in question, this is the value of the function at ##X=(x,y)## when ##x\neq0##, and ##f(X)=0## when ##X=(0,y)## for any ##y## even ##y=0##.
Now, along any vector or line from the origin the directional derivative ##f'(Y,0)## (where ##Y=(a,b)## is...
I was trying to derive current for Complex Scalar Field and I ran into the following:So we know that the Lagrangian is:
$$L = (\partial_\mu \phi)(\partial^\mu \phi^*) - m^2 \phi^* \phi$$
The Lagrangian is invariant under the transformation:
$$\phi \rightarrow e^{-i\Lambda} \phi $$ and $$\phi^*...
Hello everybody.
I have a free scalar in two dimensions. I know that its propagator will diverge for lightlike separations, that is t= ±x. I have to find the prefactor for this delta function, and I don't know how to do this.
How do I see from, for example, \int \frac{dk}{\sqrt{k^2+m^2}} e^{i k...
If a question asks for the direction of the maximum gradient of a scalar field, is it acceptable to just use del(x) as the answer or is the question asking for a unit vector?
Thanks
Homework Statement
Consider the Lagrangian, L, given by
L = \partial_{\mu}\phi^{*}(x)\partial^{\mu}\phi(x) - m^2\phi^{*}(x)\phi(x) .
The conjugate momenta to \phi(x) and \phi^{*}(x) are denoted, respectively, by \pi(x) and \pi^{*}(x) . Thus,
\pi(x) = \frac{\partial...
Homework Statement
Silly question, but I can't seem to figure out why, in e.g. Peskin and Schroeder or Ryder's QFT, the Fourier transform of the (quantized) real scalar field \phi(x) is written as
\phi (x) = \int \frac{d^3k}{(2\pi)^3 2k_0} \left( a(k)e^{-ik \cdot x} + a^{\dagger}(k)e^{ik...
I am having some problem with this attached question. I also attached my answer...
My problem is the appearence of the term:
2 e (A \cdot \partial C) |\phi|^2
which shouldn't appear...but comes from cross terms of the:
A \cdot A \rightarrow ( A + \partial C) \cdot (A + \partial C)
In my...
I would like to ask something.
How is the solution of EOM for the action (for FRW metric):
S= \int d^{4}x \sqrt{-g} [ (\partial _{\mu} \phi)^{2} - V(\phi) ]
give solution of:
\ddot{\phi} + 3H \dot{\phi} + V'(\phi) =0
I don't in fact understand how the 2nd term appears... it...
To every scalar field s(x,y) there corresponds a 'constant' vector field x = A s(x,y) and y = B s(x,y), where A,B are direction cosines. The vector field is only partially constant since only the directions, and not the magnitudes, which are equal to |f(x,y)|, of the field vectors are constant...
Question: For the scalar field \Phi = x^{2} + y^{2} - z^{2} -1, sketch the level surface \Phi = 0 . (It's advised that in order to sketch the surface, \Phi should be written in cylindrical polar coordinates, and then to use \Phi = 0 to find z as a function of the radial coordinate \rho)...
A scalar field \psi is dependent only on the distance r = \sqrt{x^{2} + y^{2} + z^{2}} from the origin.
Show:
\partial_{x}^{2}\psi = \left(\frac{1}{r} - \frac{x^{2}}{r^{3}}\right)\frac{d\psi}{dr} + \frac{x^{2}}{r^{2}}\frac{d^{2}\psi}{dr^{2}}
I've used the chain and product rules so...
If a vector field can be decomposed how a sum of a conservative + solenoidal + harmonic field...
so, BTW, a scalar field can be decomposed in anothers scalar fields too?
Hello All,
In Carroll's there is a brief introduction to a dynamical dark energy in which the equation of motion for slowly rolling scalar field is discussed.
Then to give an idea about the mass scale of this field it is compared to the Hubble constant, saying that it has an energy of...
Can you please tell me whether I am right or wrong?
Lagrangians are scalars. They are NOT invariant under coordinate transformations[ the simplest example is when you have a gravitational potential(V=mgz) and you translate z by "a"(some number)...
Homework Statement
Evaluate the scalar field ##f(r, \theta, \phi)= \mid 2\hat{r}+3\hat{\phi} \mid## in spherical coords.
Homework Equations
Law of Cosines?
##\mid \vec{A} + \vec{B} \mid = \sqrt{A^2+B^2+2ABCos(\theta)}##
The Attempt at a Solution
I'm not sure the law of cosines...
Good afternoon fellow scientists,i have a small problem in evaluating the propagator for the complex Klein-Gordon field. Although the procedure is the one followed for the computation of the propagator of the real K-G field, a problem comes up:
As known: <0|T\varphi^{+}(x)\varphi(y)|0> =...
I hope this fits this section. This doesn't all fit into the title, but this comes from a homework on conformal field theory, and I am slightly stumped on it. I just can't seem to get anything sensible out of it at the end, but it may be because I've just done something wrong (even though I've...
Homework Statement
Show that
[\hat{\phi}(x_1),\hat{\phi}^\dagger(x_2)] = 0
for (x_1 - x_2)^2 < 0
where \phi is a complex scalar field
Homework Equations
\hat{\phi}=\int\frac{d^3 \mathbf{k}}{(2\pi)^3 \sqrt{2\omega}}[\hat{a}(k)e^{-ik\cdot x} + b^\dagger(k)e^{ik\cdot x}]...
Sorry for reopening a closed thread. But I have exactly the same doubt as this guy: https://www.physicsforums.com/showthread.php?t=346730
And the answer doesn't actually answer his question. I do get delta(p+p'), but they just help me in getting a_{p}a_{-p} and a_{p}^{\dagger}a_{-p}^{\dagger}...
Homework Statement
I am studying inflation theory for a scalar field \phi in curved spacetime. I want to obtain Euler-Lagrange equations for the action:
I\left[\phi\right] = \int \left[\frac{1}{2}g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi + V\left(\phi\right) \right]\sqrt{-g} d^4x
Homework...
Hello!
Im currently reading Ryder's QFT book and am confused with the variation of a scalarfield.
He writes that the variation can be done in two ways,
\phi(x) \rightarrow \phi'(x) = \phi(x) + \delta \phi(x)
and
x^\mu \rightarrow x'^\mu = x^\mu + \delta x^\mu.
This seems...
I have been trying to get my head around this topic for a while. As I go through the description of scalar fields, the inflation and the potential inflaton, (in description as in ned.ipac.caltech.edu), I constantly miss a concept. There must be a fundamental difference between the type of...
Hi to all! I have the following transformation
\tau \to \tau' = f(\tau) = t - \xi(\tau).
Also I have the action
S = \frac{1}{2} \int d\tau ( e^{-1} \dot{X}^2 - m^2e)
where e = e(\tau) . Then in the BBS String book it says that
$$ {X^{\mu}}' ({\tau}') = X^{\mu}(\tau)$$
and...
as i understand it the higgs field is a spin-0 scalar field that gives mass to elementry particles. How is it a scalar field? I thought it was homogenous.
Hi can I just check that i haven't done anyhting foolish here whe quantising the scalar field;
\ddot{\phi} - \frac{1}{a^2}\nabla \phi + 3H\dot{\phi} - 3\frac{H}{a^2}\nabla \phi + m^2 \phi
with \phi = \int \frac{d^3 K}{(2\pi)^{\frac{3}{2}}}(\chi \exp(+ikx) +\chi \dagger \exp(-ikx))...
According to Carroll, \nabla \phi is covariant under rotations. This really confuses me. For example, how could equations like \vec{F}=-\nabla V be rotationally covariant if force is a contravariant vector?
I know this is strictly speaking more of a mathy question, but I still figured this...
Here and there I come across the following formula for the Lagrangian density of a real scalar field, but not a deriviation.
\mathcal{L} = \frac {1}{2} [ \dot \phi ^2 - ( \nabla \phi ) ^2 - (m \phi )^2 ]
Could someone show me where this comes from? The m squared term in particular...
i am trying to understand how to express contractions of field operators via propagators.
we are talking about an interacting theory of 2 complex scalar fields,
lets call them ψ1 and ψ2.
the interaction term is: Lint=λ(ψ2)^3(ψ1)
i have found the free propagator defined as...
"Quantum" gravity -- Planck's constant as a scalar field?
I was just reading about a fascinating new theory on the solution to the quantum gravity problem:
http://arxiv.org/pdf/1212.0454.pdf
I really like it, but I have one big problem with it:
The author states that
G = \frac{\hbar...
Homework Statement
For some scalar field f : U ⊆ Rn → R, the line integral along a piecewise smooth curve C ⊂ U is defined as
\int_C f\, ds = \int_a^b f(\mathbf{r}(t)) |\mathbf{r}'(t)|\, dt
where r: [a, b] → C is an arbitrary bijective parametrization of the curve C such that r(a) and r(b)...
Hi.
Let's say we have a complex scalar field \varphi and we separate it into the real and the imaginary parts:
\varphi = (\varphi1 + i\varphi2)
It's Lagrangian density L is given by:
L = L(\varphi1) + L(\varphi1)
Can you tell the argument behind the idea that in summing the densities of...
Homework Statement
Hi I a attempting to derive the expression for the conserved Noether charge for a free complex scalar field.
The question I have to complete is: " show, by using the mode expansions for the free complex scalar field, that the conserved Noether charge (corresponding to complex...
One point about Wick rotation is puzzling me and I can not find explanations in books. It concerns the invariants formed from scalar product and solutions to equation. So I will expose my way of reasoning to let you see if it is correct and at the end ask more specific questions.
Let's start...
Homework Statement
Homework Equations
Definitely related to the divergence theorem (we're working on it):
The Attempt at a Solution
I'm a bit confused about multiplying a scalar field f into those integrals on the RHS, and I'm not sure if they can be taken out or not. If they can be, I...
Hi all,
I'm a part III student and taking the QFT course. The following seems "trivial" but when I went and asked the lecturer, the comment was that they too hate such nitty gritty details!
The problem is page 12 of Tong's notes: http://www.damtp.cam.ac.uk/user/tong/qft/one.pdf
All...
Which is the mass dimension of a scalar filed in 2 dimensions?
In 4 dim I know that a scalar field has mass dimension 1, by imposing that the action has dim 0:
S=\int d^4 x \partial_{\mu} A \partial^{\mu} A
where
\left[S\right]=0
\left[d^4 x \right] =-4
\left[ \partial_{\mu} \right]=1...
Homework Statement
I have the following task:
In quantum free scalar field theory find commutators of creation and anihilation operators with total four-momentum operator, starting with commutators for fields and canonical momenta. Show that vacuum energy is zero.
Homework Equations...
Homework Statement
I understand the premise of Noether's theorem, and I've read over it in as many online lectures as I can find as well as in An Introduction to Quantum Field Theory; Peskin, Schroeder but I can't seem to figure out how to actually calculate it. I feel like I'm missing a...
We all know that for the gravitational field we can write the Poisson Equation:
\nabla^2\phi=-4\pi G\rho
But I was wondering if, mathematically, we can write the same equation for a scalar field which scale as r^{-2}.
Here is the thing. When you deal with gravity, the Poisson equation is...
How to prove that \nabla x (\phi\nabla\phi) = 0?
(\phi is a differentiable scalar field)
I'm a bit confused by this "differentiable scalar field" thing...
Okay this might be a nooby question, but it bothers me.
What is the difference between the line integral of a scalar field and just a regular integral over the scalar field?
For a function of one variable i certainly can't see the difference. But then I thought they might be identical in...
Homework Statement
Consider the scalar field
V = r^n , n ≠ 0
expressed in spherical coordinates. Find it's gradient \nabla V in
a.) cartesian coordinates
b.) spherical coordinates
Homework Equations
cartesian version:
\nabla V = \frac{\partial V}{\partial x}\hat{x} +...