标题： 从半经典形式主义中得出的极端相对论气泡上的热压 显示英文标题

标题： Thermal pressure on ultrarelativistic bubbles from a semiclassical formalism

摘要： 我们研究一个在热等离子体中以超相对论速度运动的平面气泡壁。 这种情况可能出现在早期宇宙的一阶电弱相变过程中。 当粒子穿过壁时，假设它们的质量从$m_a$增加到$m_b$，并且它们被减速，导致它们发射无质量辐射（$m_c=0$）。 我们关注的是传递给壁的动量、壁所感受到的热压强以及壁的最终速度。 我们采用半经典电流辐射（SCR）形式来执行这些计算。 入射的带电粒子被当作点状的经典电磁电流处理，量子电磁辐射（光子）的谱由计算适当的矩阵元得到。 为了理解谱如何依赖于壁的厚度，我们探讨了对应于突然减速和渐进减速的简化电流模型。 对于突然减速的模型，我们发现SCR形式可以再现以前工作中假设辐射是软的情况下得到的$P_\mathrm{therm} \propto \gamma_w^0$标度，但如果辐射不是软的，SCR形式可以用来获得$P_\mathrm{therm} \propto \gamma_w^2$。 对于渐进减速的模型，我们发现壁的厚度$L_w$会截断在动量为$\sim \gamma_w^2 / L_w$以上的原本平坦的对数辐射谱，并讨论与经典电磁制动辐射的联系。 显示英文摘要

摘要： We study a planar bubble wall that is traveling at an ultrarelativistic speed through a thermal plasma. This situation may arise during a first-order electroweak phase transition in the early universe. As particles cross the wall, it is assumed that their mass grows from $m_a$ to $m_b$, and they are decelerated causing them to emit massless radiation ($m_c=0$). We are interested in the momentum transfer to the wall, the thermal pressure felt by the wall, and the resultant terminal velocity of the wall. We employ the semiclassical current radiation (SCR) formalism to perform these calculations. An incident-charged particle is treated as a point-like classical electromagnetic current, and the spectrum of quantum electromagnetic radiation (photons) is derived by calculating appropriate matrix elements. To understand how the spectrum depends on the thickness of the wall, we explore simplified models for the current corresponding to an abrupt and a gradual deceleration. For the model of abrupt deceleration, we find that the SCR formalism can reproduce the $P_\mathrm{therm} \propto \gamma_w^0$ scaling found in earlier work by assuming that the emission is soft, but if the emission is not soft the SCR formalism can be used to obtain $P_\mathrm{therm} \propto \gamma_w^2$ instead. For the model of gradual deceleration, we find that the wall thickness $L_w$ enters to cutoff the otherwise log-flat radiation spectrum above a momentum of $\sim \gamma_w^2 / L_w$, and we discuss the connections with classical electromagnetic bremsstrahlung.