Abstract
An $I$-ball/oscillon is a solitonlike oscillating configuration of a real scalar field, and defined as a minimum energy state for a given adiabatic invariant. It lasts for a long time because of the approximate conservation of their adiabatic invariant. In this paper, we examine the stability of a special type of $I$-ball/oscillon, the ``exact'' $I$-ball/oscillon, whose adiabatic invariant is exactly conserved. We show that the exact $I$-ball/oscillon is generally stable in classical field theory, but one with a certain adiabatic invariant is unstable against small perturbations because fluctuations around the exact $I$-ball/oscillon profile have instability bands. Accordingly, the exact $I$-ball/oscillon breaks up in the presence of the fluctuations of corresponding instability modes. We also confirm the fragileness of the exact $I$-ball/oscillon by the classical lattice simulation.
Highlights
An I-ball/oscillon [1,2,3] is a nontopological solitonlike solution of a real scalar field coherently oscillating around the minimum of the potential
A lot of studies on I-balls/oscillons indicate that the lifetime of I-balls/ oscillons is extremely long [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. This longevity is theoretically interesting and motivates phenomenological study (See, e.g., Refs. [28,29,30] for gravitational waves from I-balls/oscillons and Ref. [31].). This lump of a real scalar field is theoretically defined as a minimum energy state of a given adiabatic invariant [13,32]
The reason for the longevity of I-balls/oscillons is the approximate conservation of the adiabatic invariant I, which is regarded as the particle number conservation [33]
Summary
An I-ball/oscillon [1,2,3] is a nontopological solitonlike solution of a real scalar field coherently oscillating around the (local) minimum of the potential. A lot of studies on I-balls/oscillons indicate that the lifetime of I-balls/ oscillons is extremely long [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27] This longevity is theoretically interesting and motivates phenomenological study It is generally difficult to carry out the Floquet analysis around the oscillating background which has a spatial dependence, only for the exact I-ball/oscillon case, we can reveal the nonperturbative phenomenon We confirm this decay process of the exact I-ball/oscillon by the classical lattice simulation.
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