cpt theorem, 10 mcqs on it with explained answers
Here are 10 multiple-choice questions on the CPT theorem, each with an explained answer:
1. What does the CPT theorem state in quantum field theory?
a) Physical laws are invariant under simultaneous charge conjugation, parity, and time reversal
b) Physical laws only conserve charge and parity
c) Physical laws violate time reversal symmetry
d) Physical laws depend on the direction of time
Answer: a) Physical laws are invariant under simultaneous charge conjugation, parity, and time reversal
Explanation: CPT theorem guarantees that combined CPT transformations leave all physical laws invariant.
2. Which symmetries does the CPT theorem combine?
a) Charge conjugation (C), parity (P), and time reversal (T)
b) Charge conjugation and lepton number
c) Parity and angular momentum
d) Time reversal and momentum
Answer: a) Charge conjugation (C), parity (P), and time reversal (T)
Explanation: CPT combines these three fundamental discrete symmetries.
3. According to the CPT theorem, which of the following can never happen?
a) CPT violation leading to different behaviors of matter and antimatter under CPT
b) Conservation of energy
c) Change in lepton number
d) Violation of charge conservation
Answer: a) CPT violation leading to different behaviors of matter and antimatter under CPT
Explanation: CPT theorem asserts that CPT symmetry cannot be violated in local quantum field theories.
4. What consequence does CPT symmetry have for the masses of particles and antiparticles?
a) They must be equal
b) Particles are always heavier
c) Masses differ by a charge factor
d) Antiparticles lack mass
Answer: a) They must be equal
Explanation: CPT symmetry requires particles and their antiparticles to have the same mass.
5. What happens to spin under the time reversal part of CPT?
a) It remains unchanged
b) It reverses direction
c) It doubles
d) It becomes zero
Answer: b) It reverses direction
Explanation: Time reversal flips spin and momentum directions.
6. In which type of theories is the CPT theorem strictly valid?
a) Local, Lorentz-invariant quantum field theories
b) Classical mechanics
c) Non-relativistic quantum mechanics only
d) String theories without Lorentz invariance
Answer: a) Local, Lorentz-invariant quantum field theories
Explanation: The CPT theorem relies on locality and Lorentz invariance.
7. What experimental evidence supports CPT invariance?
a) Equal mass and lifetime of particles and antiparticles
b) Parity violation in weak interactions
c) Charge non-conservation
d) Neutrino oscillations
Answer: a) Equal mass and lifetime of particles and antiparticles
Explanation: Precise tests show particles and antiparticles behave as CPT predicts.
8. Which individual symmetries are known to be violated separately but CPT is preserved?
a) C, P, and T
b) Energy, mass, and charge
c) Spin and momentum
d) Angular momentum and baryon number
Answer: a) C, P, and T
Explanation: Weak interactions violate C, P, and CP, but combined CPT remains conserved.
9. Which statement describes the CPT operator?
a) It is anti-unitary and anti-linear
b) It is unitary and linear
c) It only affects time coordinate
d) It is a continuous symmetry operator
Answer: a) It is anti-unitary and anti-linear
Explanation: CPT involves time reversal, making it anti-linear and anti-unitary.
10. Which of the following would indicate new physics beyond the Standard Model?
a) Observation of CPT violation
b) Parity violation in weak interactions
c) Conservation of baryon number
d) Equality of particle and antiparticle masses
Answer: a) Observation of CPT violation
Explanation: CPT violation would challenge fundamental assumptions of quantum field theory.
