Massless particles, such as photons (particles of light), are fundamental particles in physics. They do not require any subcomponents to make them up in the same way that composite particles (made up of other particles) do. In other words, they do not consist of smaller particles with zero mass.
Massless particles are described within the framework of quantum field theory, where particles are associated with excitations of underlying fields. Photons, for example, are quanta of the electromagnetic field. In this framework, the mass of a particle is related to how the associated field interacts with the Higgs field, which gives particles their mass. For a particle to be massless, its associated field must not interact with the Higgs field in a way that would give it mass.
Particles like photons are indeed observed to be massless or have very small masses compared to other particles like electrons or quarks. Their masslessness is a fundamental property, and they do not require any constituent particles with zero mass to exist. Instead, they are elementary particles in their own right.
It's worth noting that while massless particles exist without the need for constituent particles with zero mass, their interactions and behaviors can be described and understood using mathematical frameworks like quantum field theory and general relativity. These theories provide a comprehensive description of the properties and behavior of massless particles within the context of modern physics.