Relativistic quantum theory shows that the known Einstein time dilation (ED) approximately holds for the decay law of the unstable particle having definite momentum p (DP). I use a different definition of the moving particle as the state with definite velocity v (DV). It is shown that in this case the decay law is not dilated. On the contrary, it is contracted as compared with the decay law of the particle at rest. It is demonstrated that ED fails in both DP and DV cases for time evolution of the simple unstable system of the kind of oscillating neutrino. Experiments are known which show that ED holds for mesons. The used theory may explain the fact by supposing that the measured mesons are in DP state.
Relativistic quantum theory shows that the known Einstein time dilation (ED) approximately holds for the decay law of the unstable particle having definite momentum p (DP). I use a different definition of the moving particle as the state with definite velocity v (DV). It is shown that in this case the decay law is not dilated. On the contrary, it is contracted as compared with the decay law of the particle at rest. It is demonstrated that ED fails in both DP and DV cases for time evolution of the simple unstable system of the kind of oscillating neutrino. Experiments are known which show that ED holds for mesons. The used theory may explain the fact by supposing that the measured mesons are in DP state.
The relativistic quantum decay laws of moving unstable particles are analyzed for a general class of mass distribution densities which behave as power laws near the (nonvanishing) lower bound μ0 of the mass spectrum. The survival probability Pp(t) , the instantaneous mass Mp(t) , and the instantaneous decay rate Γp(t) of the moving unstable particle are evaluated over short and long times for an arbitrary value p of the (constant) linear momentum. The ultrarelativistic and nonrelativistic limits are studied. Over long times, the survival probability Pp(t) is approximately related to the survival probability at rest P0(t) by a scaling law. The scaling law can be interpreted as the effect of the relativistic time dilation if the asymptotic value Mp∞ of the instantaneous mass is considered as the effective mass of the unstable particle over long times. The effective mass has magnitude μ0 at rest and moves with linear momentum p or, equivalently, with constant velocity 1/1+μ02/p2 . The instantaneous decay rate Γp(t) is approximately independent of the linear momentum p , over long times, and, consequently, is approximately invariant by changing reference frame.
We study the decay law for a moving unstable particle. The usual time-dilatation formula states that the decay width for an unstable state moving with a momentum p and mass M is Γ~p=ΓM/p2+M2 with Γ being the decay width in the rest frame. In agreement with previous studies, we show that in the context of QM as well as QFT this equation is \textit{not} correct provided that the quantum measurement is performed in a reference frame in which the unstable particle has momentum p (note, a momentum eigenstate is \textit{not} a velocity eigenstate in QM). We then give, to our knowledge for the first time, an analytic expression of an improved formula and we show that the deviation from Γ~p has a maximum for p/M=2/3, but is typically \textit{very} small. Then, the result can be easily generalized to a momentum wave packet and also to an arbitrary initial state. Here, we give a very general expression of the non-decay probability. As a next step, we show that care is needed when one makes a boost of an unstable state with zero momentum/velocity: namely, the resulting state has zero overlap with the elements of the basis of unstable states (it is already decayed!). However, when considering a spread in velocity, one finds again that Γ~p is typically a very good approximation. The study of a velocity wave-packet represents an interesting subject which constitutes one of the main outcomes of the present manuscript.\textbf{ }In the end, it should be stressed that there is no whatsoever breaking of special relativity, but as usual in QM, one should specify which kind of measurement on which kind of state is performed.
According to the classical special theory of relativity any nonstationary system moving with velocity v must evolve (e.g., decay) 1/γ times slower than the system at rest, γ = (1 − v 2) −1/2 (the Einstein retardation ER). Quantum mechanics allows one to calculate the evolution of both systems separately and to compare them thus verifying ER. It is shown here that ER is not valid for a simple system: the spreading packet of the free spinless particle. Earlier it was shown that ER does not hold for some other systems. So one may state Experiments show that moving unstable particles (e.g., µ-mesons, π-mesons) decay slower than the particles at rest. More explicitly, let N0(t) = N exp(−t/τ0) be the decay law of the particles at rest, τ0 being life-time. Then the life time of particles moving with velocity v is τv = τ0γ, γ = (1 −v 2) −1/2, and the decay
Abstract The transformation of canonical decay laws of moving unstable quantum systems is derived from the basic principles of quantum theory and special relativity by approximating, over intermediate times, the decay laws at rest with superpositions of exponential modes via the Prony analysis. The survival probability , which is detected in the laboratory reference frame where the unstable system moves with constant linear momentum p , is represented by the transformed form of the survival probability at rest . The transformation of the intermediate times, which is induced by the change of reference frame, is obtained by evaluating the function . Under determined conditions, this function grows linearly and the survival probability transforms, approximately, according to a scaling law over an estimated time window. The relativistic dilation of times holds, approximately, over the time window if the mass of resonance of the mass distribution density is considered to be the effective mass at rest of the moving unstable quantum system.
Abstract The decay of a moving system is studied in case the system is initially prepared in a superposition of two, approximately orthogonal, unstable quantum states. The survival probability is evaluated over short and long times in the reference frame where the unstable system moves with constant linear momentum p . The mass distribution densities, which describe the two unstable states of the superposition, exhibit thresholds near the non-vanishing lower bounds and of the mass spectra. If these lower bounds coincide, the long-time survival probability shows a dominant inverse-power-law decay and is approximately related to the survival probability at rest via a time dilation. The scaling factor reads . If the lower bounds and differ, damped oscillations of the survival probability appear over long times and the scaling relation is lost. These oscillations are enveloped in an inverse-power-low profile which is determined by the thresholds. By changing reference frame, the period T 0 of the oscillations at rest transforms in the longer period T p according to a factor which is the weighted mean of the factors and , with non-normalized weights and . The oscillations tend to vanish in the ultrarelativistic limit.