Quantum Field Theory (QFT) is the theoretical framework describing the quantisation of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high energy physics as well as condensed matter physics and closely related to statistical field theory. Use ...

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effective field theory of the projective semion model

The "projective semion" model was considered in http://arxiv.org/abs/1403.6491 (page 2). It is a symmetry enriched topological (SET) phase. There is one non-trivial anyon, a semion $s$ which induces a ...
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1answer
60 views

Concerning The Oil Drop Experiment: How does ionizing radiation create the electron(s) that the droplets of oil collect?

Concerning the Oil Drop Experiment: I read, “Ionizing radiation is used to create the electron that the droplets of oil collect. When the air in the apparatus is bombarded by this ionizing radiation ...
9
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3answers
661 views

What does Weinberg–Witten theorem want to express?

Weinberg-Witten theorem states that massless particles (either composite or elementary) with spin $j > 1/2$ cannot carry a Lorentz-covariant current, while massless particles with spin $j > 1$ ...
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2answers
52 views

Where is the BRST symmetry?

When quantizing YM we start from the gauge fixed path integral (to remove redundancy of integrating over Gauge symmetric configurations) $$\int \mathcal{D}A \delta(G(A)) \text{det} \Delta_{FP}e^{i\int ...
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26 views

Longitudinal Polarization and Spin-0 for Massive Vector Fields

I was wondering if anybody would be willing to explain how a plane wave solution of the form $\vec{B^\mu}=\epsilon^\mu{e^{k_0ct+\vec{k}.\vec{x}}}$ for a massive vector field's equations, say for ...
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1answer
265 views
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1answer
51 views

Anomalies and determinant bundle curvature

I heard that anomalies and curvature of determinant bundle are related. Namely, curvature of determinant bundle is related to Chern-Simons form (which are involved in description of gauge anomalies). ...
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1answer
74 views

Could Dark energy and Dark matter just simply be a warping of spacetime? [closed]

Why do most theories about what Dark energy and Dark matter is make it so that these substances (or not) need to be some kind of undiscovered particle? Would it be possible for Dark energy to simply ...
3
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2answers
262 views

From the viewpoint of field theory and Derrick's theorem, what's the classical field configuration corresponding to particle? Is it a wavepacket?

In the framework of QM, we have known that particle, like electron, cannot be a wavepacket, because if it is a wavepacket then it will become "fatter" due to dispersion and it's impossible. However ...
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60 views

Logarithms in Renormalization

I am learning renormalization in Quantum field theory and following mainly Schwartz (Quantum field theory and standard model) for it. While explaining Renormalization group equations it says it mainly ...
4
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1answer
432 views

Lorentz-invariant phase space of a three-body decay process

I am not following the use of delta function in the 3-body decay process. In $\gamma^* \to gq\bar{q}$ process, with $\gamma^*$ being a virtual photon, we have a phase space factor $$d^9R_3 = ...
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1answer
29 views

Conformational Analysis of Ethane and Butane

How does a condensed matter theorist explain conformations of Ethane and Butane using tools from Quantum field theory? If they don't how do they calculate energy differences and predict differences ...
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5answers
6k views

What is meant by “Nothing” in Physics/Quantum Physics?

I am not a phycisist, so please forgive my ignorance. This is related to my posts and this. I am trying to understand what is meant by the term "Nothing" in physics or Quantum Field Theory (QFT) since ...
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0answers
29 views

Symmetry breaking with adjoint matter, departing from vacuum in different way

$$L=-\frac{1}{4}TrF_{\mu\nu}F^{\mu\nu}+\frac{1}{2}D_\mu\phi D^\mu \phi -\lambda V(\phi)$$ Say we have a potential $V(\phi)=(|\phi|^2-v^2)^2$, and 3-component real scalar field $\phi=(\phi_1, \phi_2, ...
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0answers
22 views

Interesting question regarding stimulated emission

why is outgoing photon emitted during stimulated emission in phase with the incoming photon? I can't see why this is so because the two photons may be out of phase yet conserving momentum and energy. ...
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0answers
28 views

Functional Gaussian Integral Involving Gradient Square with non-trivial Kernel

I have been trying to solve the following functional gaussian integral. I've had problem finding the inverse kernel. $f(x)$ and $\rho(x)$ are two known scalar fields and they do vanish at infinity. ...
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1answer
132 views

Invariance in Euclidean and Minkowski spaces

Consider Wick's rotation from Minkowski to Euclidean space in QFT. What is the connection between O(4) invariance in Euclidean space and Lorentz invariance in Minkowski space? If we define a quantity ...
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0answers
23 views

The seesaw mechanism and block-diagonalization

I encounter a description about the diagonization in seesaw mechanism. I think it is somewhat elementary in linear algebra, but I can not understand it well. The description is as follows. In the ...
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1answer
184 views

Why can we not choose the stress tensor in a CFT to be identically symmetric?

The stress tensor for a conformal field theory (or any quantum field theory) can be derived from the action $S$ by the functional derivative $$T^{\mu \nu} ~=~ -\frac{2}{\sqrt{|g|}}\frac{\delta ...
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1answer
62 views

Issues of normalization & differential final state momenta in analysis of normalized differential quantum-field-theoretic probability of scattering

The normalized differential quantum-field-theoretic probability $dP$ of scattering is given by $$dP=\frac{|\langle f |S|i\rangle|^{2}}{\langle f|f\rangle\langle i|i\rangle}d\Pi,$$ where $|i\rangle$ ...
0
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1answer
36 views

Information that can be extracted from the time-ordered correlation function

The time-ordered correlation function can be very complicated and encodes a tremendous amount of information. For example, the LSZ formula can be used to extract S-matrix elements from the ...
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0answers
29 views

Comparison of vacua and annihilation operators of Klein-Gordon theory and phi-fourth theory

The ground state or vacuum of an interacting theory is, in general, different from the ground state or vacuum of a free theory. In what cases are the two vacuums the same as each other? Can an ...
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1answer
42 views

Alternatives to scattering experiments

Scattering experiments have been a fruitful and efficient way to determine the particles that exist in nature and how they interact. What are some of the other experimental techniques used to ...
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2answers
76 views

Interacting Hamiltonian commutes with momentum operator?

In Peskin's textbook chapter 7 Radiative Corrections: some formal developments (page 212 second paragraph), he describes two-point functions and chooses states to be eigenstates of the full ...
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1answer
40 views

Why is $\sqrt{v_1+v_2+\ldots} =246$ GeV in multi-Higgs models?

Where does the condition come from that in models with several electroweak breaking doublets the square root of the squared sum of the VEVs should yield $246$ GeV?
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1answer
51 views

Can a symmetry breaking VEV lie far above the “symmetry breaking scale?”

The scale where some symmetry gets broken can be computed using the renormalization group equations for the gauge couplings. If there is only one Higgs VEV responsible for some breaking, can this VEV ...
5
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1answer
74 views

How to understand the idea of functional renormalization group?

I have been looking at how to use the functional RG method in many-body systems, but I don't quiet get the idea of it, it look different from Wilson's RG approach (eg. why shall we integrate out the ...
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23 views

What are the Higgs masses for $SU(2) \times U(1)$ goes to $U(1)$ symmetry breaking with a complex triplet?

Consider an $SU(2)\times U(1)_Y\rightarrow U(1)_{EM}$ theory that is broken via a complex triplet with hypercharge 2. The potential is of the form \begin{align} V(\Phi) = -m^2\Phi^\dagger\Phi + ...
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1answer
83 views

Why is the $D^0$ oscillation so different from the $K^0$ and $B^0$?

I have looked for this answer into many articles and books but I am not able to figure out why $D^0\to\bar{D}^0$ is so highly suppressed if compared to the $B^0 \to \bar{B}^0$ and $K^0 \to \bar{K}^0$ ...
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0answers
87 views

Why are photons massless (quantum field theory) [duplicate]

I'm really trying to understand Quantum field theory and gauge in-variance, I'd like to ask a question about this to aid my understanding. The QED lagrangian as below has a kinetic term for this gauge ...
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0answers
44 views

What is a good mathematical introduction to QFT [duplicate]

I've noticed that, any time I try to pick up Peskin and Schroeder, the main stumbling block it the leap in mathematical constructs from QM. Is there a good textbook that could teach me some of the ...
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2answers
44 views

Momentum conserving delta-function in the transfer matrix of quantum-field-theoretic scattering theory

The $S$-matrix vanishes unless the initial and final states have the same total $4$-momentum, so it is helpful to factor an overall momentum-conserving $\delta$-function: ...
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1answer
99 views

Can I catch a particle (such as electron) and say it's left hand

Why is only the left hand electron coupled to weak interaction? How can I tell the chirality of an electron?
3
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1answer
69 views

Why doesn't the four-gluon vertex give mass to gluons?

We have a four-gluon vertex and a gluon vacuum condensate. Why doesn't this provide us with gluon masses, as in the NJL model where the condensate gives rise to an effective mass term?
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11answers
12k views

Quantum Field Theory from a mathematical point of view

I'm a student of mathematics with not much background in physics. I'm interested in learning Quantum field theory from a mathematical point of view. Are there any good books or other reference ...
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0answers
26 views

Applying AdS-CFT to traversable wormholes? [closed]

ER=EPR recently brought up the connection between non-traversable wormholes and entanglements. What about traversable wormholes? Can we apply AdS/CFT to traversable wormholes?
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Why do people say that the Higgs mechanism gives mass to the gauge bosons without mentioning the fermions?

Many presentations of the Higgs mechanism only explain it as giving mass to the $W$ and $Z$ gauge bosons, but don't mention the quarks or charged leptons. For example: ...
4
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1answer
68 views

Why use coherent state path integral? What is its motivation or goal?

In almost all textbooks of quantum field theory for high energy, they insert the position and momentum eigenstate to formulate the path integral. While in condensed matter field theory, they insert ...
6
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2answers
309 views

Why does the non-linearity of the string action prohibit stretching due to strong excitations?

From 't Hooft's String Theory lecture notes on page 8 (paraphrased): To understand hadronic particles as excited states of strings, we have to study the dynamical properties of these strings, and ...
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0answers
29 views

Antiunitary operators in the tenfold way

In the classification of free fermion systems in condensed matter, physicists usually divide the systems into ten symmetry classes, first discovered by Altland and Zirnbauer. In their classification, ...
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4answers
3k views

Decay of massless particles

We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
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1answer
49 views

Magnetic monopoles gauge theories

I'm quoting 't Hooft: "[...] Locally stable field configurations may exist that have some topological twist in them [...].Careful analysis of the existing Lie groups and the way they may be ...
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0answers
45 views

Electromagnetic waves and photons? [duplicate]

Electromagnetic waves are photons or photons cause electromagnetic waves ? Its said that when charges are accelerated we get electric and magnetic field that carries energy but then they say that this ...
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2answers
67 views

Electromagnetic Radiation and Communication!

I read that the accelerated charges create electromagnetic field/spectrum which consists of following different waves: gamma, X-rays, ultraviolet, visible light, infrared, microwaves, & radio ...
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0answers
27 views

scalar field boundary condition in background with U(1) isometry

I have a simple question about Lewkowycz and Maldacena's paper In section 2, they consider the scalar field in BTZ background ground and require boundary condition of the scalar field, $\phi \sim ...
4
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1answer
247 views

Do the position-momentum uncertainty and time-energy uncertainty really exist in QFT?

It is well known from the Quantum Mechanics(QM) that for a particle, there is a position-momentum uncertainty relation: $$\Delta x\cdot \Delta p\geq \frac{1}{2}\hbar,$$ which bascically can be derived ...
3
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1answer
436 views

Do we need virtual particles?

I understand the $\Delta t \cdot \Delta E \geq \hbar / 2$ relationship and the idea behind them. However, I don't understand why do we need them at all. I'm a physics undergraduate. As far as I know, ...
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2answers
596 views

Quantum entanglement definition [closed]

How can we define Quantum entanglement (in QFT)? What are the known mathematical settings and special physical (or logical) conditions of QE applied to Quantum computing?
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36 views

The $T\rightarrow \infty $ limit in quantum field theory

I am new to quantum field theory. Prior to this, I have been using quantum mechanics for a few years. I am reading the book by A. Zee, ''quantum field theory in a nutshell'', 2nd Ed.. On page 18, ...
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1answer
70 views

What gives a particle its identity?

A lot of very smart people have stitched together the standard model, and I accept it. I don't understand it, but I assume there should be a mechanism of sorts that gives a particle some fundamental ...