Tachyon Beam

Overview
Tachyon beams are one of the few directed energy weapons mechanisms used by the Dominion. Lauded for their innate FTL velocity and destructive interactions with regular matter, tachyon based weapons are one of the few non-kinetic mechanisms considered useful by the Dominion.

Origin
The weaponization of tachyons had long been theorized and speculated by humans. However, it was only until the late pre-Dominion era that experimental prototypes would be produced. Most of the resulting designs turned out to be useless, impractical, or expensive. A handful survived and could be found in the possession of a few fleets right up until the proto-Dominion.

With the multiple singularities underwent by the Dominion, these old tachyon designs were soon revisited and after extensive experimentation, the first generation of viable designs was standardized. It took a long time for tachyon weapons to prove themselves as an effective sidegrade to the already brutally effective kinetic and self-propelled weapons.

Mechanism
Tachyons are rather strange particles, possessing imaginary mass and the peculiar property of their energy being inversely proportional to their velocity (which must always stay above c, much like how ordinary particles must always stay below c). At first, one would've assumed that an FTL particle would make for a brilliant long-ranged weapon, however, research has shown almost the opposite.

For a tachyon to have substantial energy it must be as slow as possible, meaning that any weaponized form will impart as much energy as it has available onto the tachyons it creates and fire them at close to lightspeed. Thanks to Cherenkov radiation bleeding off their energy, the tachyons will then start to rapidly speed up in transit, bleeding energy in the process.

Now when you also consider the natural diffusion of beam weapons with distance, it is clear that a tachyon weapon is going to be far more effective at close ranges as it will have more momentum to transfer. However, there is another factor to be considered. Tachyons are naturally repelled by bradyons (normal particles), this repulsion is mutual and happens at the subatomic level. This means that only a small portion of a tachyon weapon is likely to actually hit a target making it even less efficient at translating the weapon's power rating onto a target. There is one hefty upside to this though- the repulsion is mutual, meaning that the bradyons on the surface of the target will also be repelled into the target, likely at relativistic velocities if the quantity and duration of the interaction was long enough. For most matter this is catastrophic and will cause small nuclear detonations to go off inside the target, likely causing more damage than the tachyons could otherwise.

This effect falls off with range, as the tachyons lose energy and get faster, they become much more likely to hit the target before any repulsion can occur, tachyons impacting directly with bradyons mutually annihilate. This will transfer momentum and destroy the surface of a target effectively but is going to overall be far less effective.

This leaves tachyon weapons in a strange niche. Most effective at closer ranges despite being repelled more, inefficient against shielding or non-bradyonic matter, fast and likely to hit at long distances but will have lost most of their effectiveness. Perhaps even more interesting is the immense difficulty in aiming such a weapon, as the firer has to account for the tachyons accelerating like a self-propelled weapon, but without the onboard guidance system that is customary of such weapons.

Usage
Tachyon beams are used exclusively by spacecraft. They fulfill a niche as a close-range anti-material weapon with greater destructiveness than kinetic variants, and as an ultra-long-range suppression weapon, far less destructive and harder to aim than a kinetic equivalent, but with a much greater velocity which can be used to wear a target down for the coup de grâce to be delivered.

Being a DEW, they do not need a propellant to be transmuted and therefore can have a very high sustained fire rate, only limited by the thermal capacity and power bandwidth of their platform.

Ultraheavy tachyon beams are less popular as scaling up the beam density has diminishing returns, and increasing the energy of the tachyons is wasteful as most of it will have to be bled off to hit anything that isn't in knife-fight range. The most effective improvement is to increase the fire rate of the weapon.