论文标题
扩展$ f（t，b）$ teparallear重力的宇宙磁场的扩增
The amplification of cosmological magnetic fields in Extended $f(T,B)$ Teleparallel Gravity
论文作者
论文摘要
观察结果表明，绘制磁场的幅度为$ \ sim 10^{ - 6} $ g，并且在$ \ sim 10 $ kpc的尺度上是均匀的。尽管它们在宇宙中广泛存在，但它们的起源仍然是一个空旷的问题。即使通过调用磁场扩增的发电机机制或压缩效果，在星系形成之前存在种子场仍然存在问题。一般相对性预测磁场演变为$ | \ m马理{b} | \ propto 1/a^{2} $的绝热减少，其中$ a $是宇宙的比例因子。除非电磁扇形的共形对称性被打破，否则它会导致很小的原始场。在本文中，我们研究了放大原始磁场的自然机制可能与扩展的触发性重力$ f（t，b）$模型有关，其中$ t $是扭转标量和$ b $边界术语。特别是，我们考虑了与重力的非最小耦合，以期在远程背景下打破了共形对称性，特别是研究边界项$ b $的作用，可以将其视为进一步的标量场。我们发现，在完全解决通货膨胀和加热时代的$ F（t，b）$场方程之后，始终可能会出现磁场的非绝热行为，并且在重新加热的时期中出现了强大的扩增。 We also compute the ratio $r=ρ_{B}/ ρ_γ$ between the magnetic energy density and the cosmic microwave energy density during inflation, in order to explain the present value $r\simeq 1$, showing that, in the slow-roll approximation, power-law teleparallel theories with $B^{n}$ have effects indistinguishable from metric theories $R^{n}$ where $R$ is Ricci曲率标量..
Observations indicate that intergalactic magnetic fields have amplitudes of the order of $\sim 10^{-6}$ G and are uniform on scales of $\sim 10$ kpc. Despite their wide presence in the Universe, their origin remains an open issue. Even by invoking a dynamo mechanism or a compression effect for magnetic field amplification, the existence of seed fields before galaxy formation is still problematic. General Relativity predicts an adiabatic decrease of the magnetic field evolving as $|\mathbf{B}|\propto 1/a^{2}$, where $a$ is the scale factor of the Universe. It results in very small primordial fields, unless the conformal symmetry of the electromagnetic sector is broken. In this paper, we study the possibility that a natural mechanism for the amplification of primordial magnetic field can be related to extended teleparallel gravity $f(T, B)$ models, where $T$ is the torsion scalar, and $B$ the boundary term. In particular, we consider a non-minimal coupling with gravity in view to break conformal symmetry in a teleparallel background, investigating, in particular, the role of boundary term $B$, which can be consider as a further scalar field. We find that, after solving exactly the $f(T,B)$ field equations both in inflation and reheating eras, a non-adiabatic behavior of the magnetic field is always possible, and a strong amplification appears in the reheating epoch. We also compute the ratio $r=ρ_{B}/ ρ_γ$ between the magnetic energy density and the cosmic microwave energy density during inflation, in order to explain the present value $r\simeq 1$, showing that, in the slow-roll approximation, power-law teleparallel theories with $B^{n}$ have effects indistinguishable from metric theories $R^{n}$ where $R$ is the Ricci curvature scalar..
