This paper explores the implications of spontaneous CPT violation in the context of the minimal standard model. The authors propose a theoretical framework for low-energy effects of spontaneous CPT violation and partial Lorentz breaking, using conventional relativistic quantum mechanics and quantum field theory in four dimensions. They develop a CPT-violating extension of the minimal standard model that could serve as a basis for establishing quantitative CPT bounds. The paper begins by discussing the symmetry of the minimal standard model, which includes CPT invariance. It notes that numerous experiments have confirmed this result, including high-precision tests using neutral-kaon interferometry. The simultaneous existence of a general theoretical proof of CPT invariance in particle physics and accurate experimental tests makes CPT violation an attractive candidate signature for non-particle physics such as string theory. The authors then discuss the assumptions needed to prove the CPT theorem, which are invalid for strings, which are extended objects. They note that a mechanism is known in string theory that can cause spontaneous CPT violation with accompanying partial Lorentz-symmetry breaking. The effect can be traced to string interactions that are absent in conventional four-dimensional renormalizable gauge theory. Under suitable circumstances, these interactions can cause instabilities in Lorentz-tensor potentials, thereby inducing spontaneous CPT and Lorentz breaking. The authors focus specifically on CPT violation and the associated Lorentz-breaking issues in a low-energy effective theory without gravity. They note that the absence of signals for CPT violation in the neutral-kaon system provides one of the best bounds on Lorentz invariance. The paper then discusses the basics of spontaneous CPT violation, including a simple model that illustrates concepts associated with CPT and Lorentz breaking. The authors consider the possibility of alternative definitions of C, P, T and Lorentz properties that could encompass the full structure of L. The paper also discusses the continuous symmetries of the model, including the effects of Lorentz transformations. The authors note that the CPT-violating terms in the model leave unaffected the usual global U(1) gauge invariance, which has conserved current j^μ = ψ̄ γ^μ ψ. Charge is therefore conserved in the model. The authors also discuss field redefinitions, noting that certain CPT-violating terms can be eliminated through field redefinitions. They note that the term L_a' in Eq. (3) is reminiscent of a local U(1) coupling, although there is no local U(1) invariance in the theory (5). They note that related issues arise for certain nonlinear gauge choices and in the context of efforts to interpret the photon as a Nambu-Goldstone boson arising from (unphysical) spontaneous Lorentz breaking. The paper then discusses relativistic quantum mechanics based on Eq. (6), with ψ regarded as a four-component wave function. The authorsThis paper explores the implications of spontaneous CPT violation in the context of the minimal standard model. The authors propose a theoretical framework for low-energy effects of spontaneous CPT violation and partial Lorentz breaking, using conventional relativistic quantum mechanics and quantum field theory in four dimensions. They develop a CPT-violating extension of the minimal standard model that could serve as a basis for establishing quantitative CPT bounds. The paper begins by discussing the symmetry of the minimal standard model, which includes CPT invariance. It notes that numerous experiments have confirmed this result, including high-precision tests using neutral-kaon interferometry. The simultaneous existence of a general theoretical proof of CPT invariance in particle physics and accurate experimental tests makes CPT violation an attractive candidate signature for non-particle physics such as string theory. The authors then discuss the assumptions needed to prove the CPT theorem, which are invalid for strings, which are extended objects. They note that a mechanism is known in string theory that can cause spontaneous CPT violation with accompanying partial Lorentz-symmetry breaking. The effect can be traced to string interactions that are absent in conventional four-dimensional renormalizable gauge theory. Under suitable circumstances, these interactions can cause instabilities in Lorentz-tensor potentials, thereby inducing spontaneous CPT and Lorentz breaking. The authors focus specifically on CPT violation and the associated Lorentz-breaking issues in a low-energy effective theory without gravity. They note that the absence of signals for CPT violation in the neutral-kaon system provides one of the best bounds on Lorentz invariance. The paper then discusses the basics of spontaneous CPT violation, including a simple model that illustrates concepts associated with CPT and Lorentz breaking. The authors consider the possibility of alternative definitions of C, P, T and Lorentz properties that could encompass the full structure of L. The paper also discusses the continuous symmetries of the model, including the effects of Lorentz transformations. The authors note that the CPT-violating terms in the model leave unaffected the usual global U(1) gauge invariance, which has conserved current j^μ = ψ̄ γ^μ ψ. Charge is therefore conserved in the model. The authors also discuss field redefinitions, noting that certain CPT-violating terms can be eliminated through field redefinitions. They note that the term L_a' in Eq. (3) is reminiscent of a local U(1) coupling, although there is no local U(1) invariance in the theory (5). They note that related issues arise for certain nonlinear gauge choices and in the context of efforts to interpret the photon as a Nambu-Goldstone boson arising from (unphysical) spontaneous Lorentz breaking. The paper then discusses relativistic quantum mechanics based on Eq. (6), with ψ regarded as a four-component wave function. The authors