### 3.5 Alternative mechanisms

The idea that a coronal loop is twisted and then carries an electric current
gave rise to several alternative mechanisms for the loop oscillations.
An LCR-circuit model developed by Zaitsev et al. (1998) explains the loop oscillations in terms of eigen
oscillations of an equivalent electric circuit, where the current is associated with the loop twist.
Approximating the magnetic loop by a thin torus and estimating the effective circuit capacitance and
inductance as
where is the speed of light, is the density inside the loop, and are the length and
cross-sectional area of the coronal part of the loop, respectively, and is the electric current along the
loop axis. The period of the oscillations is then given by the expression
As one of the physical quantities perturbed by this effect is the current (or the twist), its periodic pulsations
would be observed through the direct modulation of the gyrosynchrotron emission by the period change of
the angle between the LOS and the magnetic field in the emitting region. Also, as the periodic twist is
accompanied by perturbations of density - see Equation (26) -, the oscillations would modulate thermal
emission as well. Also, twist perturbations could modulate the loop minor radius, resembling the
sausage mode. The decay of the oscillations is normally estimated by this model to be very
small.
Khodachenko et al. (2003) applied the idea of inductive interaction of electric currents in a group of
neighbouring loops to an alternative interpretation of kink oscillations, suggesting that they are caused by
the ponderomotoric interaction of currents in groups of inductively coupled current-carrying loops. More
specifically, the ponderomotoric interaction of current-carrying magnetic loops can lead to the oscillatory
change of the loops inclination. The efficiency of coupling, the period of oscillations and the decay time are
connected with mutual inductance of different loops in the active region analysed. Also, it was pointed out
that the interaction of the oscillating loop with neighbouring loops can lead to strong damping of the
oscillations.

We would like to stress that the periods of loop oscillations described by LCR-contour models should be
longer than the Alfvén travel time along the loop, which determines the response time of the current
system, so .

Dynamic models of magnetic reconnection predict that the processes of tearing instability and
coalescence of magnetic islands occur iteratively, leading to an intermittent or impulsive bursty energy
release and particle acceleration. Tajima et al. (1987) demonstrated the possibility of oscillatory regimes in
coalescence of current carrying loops, combining a simplified 1D analytical approach and numerical
modelling. The minimal period of oscillations was found to be

where is the characteristic length of the interaction process, connected in this case with the
width of a current sheet formed at the boundary between two interacting twisted loops. These
oscillations are essentially nonlinear, and it is likely that their period is somehow connected with
amplitude.