All Questions
59
questions
3
votes
1
answer
125
views
Why can't bosonic systems have fermionic excitations?
When reading Abrikosov's book AGD, there is a statement that 'It is obvious only that a Bose system can not have excitations with half-integral spins' (page 5).
I don't understand why this is the case....
- 51
2
votes
0
answers
76
views
Different ways to understand fermions [closed]
I first learned about fermions in my atomic physics class, where the teacher said that electrons obey the Pauli exclusion principle. Later, in my quantum mechanics class, I learned about identical ...
- 368
3
votes
1
answer
83
views
Is RG fixed point always related to a second-order phase transition?
In practice, usually one of the parameters is tuned (for example temperature in 3D Ising model, which is a relevant parameter) so that it coincides with the value of RG fixed point, then RG flow make ...
- 619
2
votes
0
answers
172
views
Is there any renormalization group with infinite number of generators that does not satisify a renormalization group equation?
A generating set of a semigroup(monoid) is a subset of the semigroup set such that every element of the semigroup can be expressed as a combination (under the semigroup operation) of finitely many ...
2
votes
1
answer
121
views
Thermal ground state?
Consider a system of $N$ fermions in a periodic box $\Lambda \subset \mathbb{R}^{d}$, described by the Hamiltonian
$$H_{N} = \sum_{k=1}^{N}(-\Delta_{x_{k}}-\mu) + \lambda \sum_{i< j}V(x_{i}-x_{j}) \...
- 1,131
0
votes
0
answers
32
views
Schwinger function with and without temperature
I have always been confused with the differences and relation between many-body theory with and without temperature. Suppose I have a theory described by some Hamiltonian $H = H_{0} + V$, where $H_{0}$...
- 1,131
0
votes
0
answers
41
views
Partition function in Non-equilibrium field theory in statistical mechanics
Consider a system that described by the Hamiltonian $H(t)$, contains non-adiabatic time-dependent external fields and the evolution drives the system away from equilibrium.
Now the partition function ...
- 177
3
votes
0
answers
77
views
Question about statistical field theory
I am starting to learn statistical field theory. The "infinite number of degrees of freedom" refers to the continuous nature of field variables in field theory, where there are infinitely ...
user347949
1
vote
1
answer
222
views
Is there (emergent) higher form spontaneous symmetry breaking in classical statistical field theory?
I was wondering if there are examples of (emergent) higher form spontaneous symmetry breaking (SSB) in classical statistical physics (finite temperature). I believe the deconfined phase of gauge ...
- 978
3
votes
0
answers
61
views
Can the upper and lower critical dimensionalities of a model coincide?
Is it possible for a field theory to have the same upper and lower critical dimensions? Has this ever been observed in any model (be it condensed matter, statistical mechanics, QFT, string etc.)?
- 71
2
votes
0
answers
88
views
Did I understand RG correctly?
I am currently self-studying Renormalization Group (RG) in Condensed matter physics (in preparation for graduate school while I'm in Alternative Military Service).
While I'm writing bunch of ...
- 21
4
votes
1
answer
609
views
Is there a notion of a "Majorana boson"?
In a similar manner to how we can define Majorana fermionic operators $\gamma_j$ via
$$
c_j \propto \gamma_{2j+1} + i \gamma_{2j}^\dagger,
$$
where the $c$'s are fermionic creation/annahilation ...
- 1,544
0
votes
0
answers
172
views
Connection between the imaginary part of retarded correlation function and derivative of Fermi-Dirac distribution function
A two-particle retarded correlation function is (its derivation is not related to my question here)
$$
C^R(\omega) = \sum_{kq}\bigg(f(\epsilon_k )-f(\epsilon_{k+q} )\bigg)\frac{1}{\omega+\epsilon_k-\...
- 1,335
1
vote
1
answer
121
views
Integration range in BCS theory
In two different ways of finding the Cooper pair energy gap, the limits of integration are different, yet both give the same result.
In the first case, when working out the energy $E_{pair}$ of a ...
- 2,122
0
votes
0
answers
110
views
Technique for diagonalising this free spinless fermionic Hamiltonian?
How does one diagonalise the following Hamiltonian?
$$
H = \sum_n \epsilon_n c^\dagger_n c_n + g \sum_n (c^\dagger_n c^\dagger_{-n} + c_{-n}c_n),
$$
where $c_n$ is a spineless fermionic op. Clearly we ...
- 1,544