Massless particles, such as photons (particles of light), can exist within the framework of quantum field theory. In this context, particles are described as excitations or quanta of their corresponding quantum fields. Massless particles, by definition, have zero rest mass. However, this does not mean that they are not composed of anything at all.
According to our current understanding, particles gain their mass through interactions with the Higgs field, a fundamental field that permeates the universe. The Higgs field interacts with certain particles, such as quarks and electrons, and gives them mass. However, photons do not directly interact with the Higgs field, which is why they are massless.
In quantum field theory, particles are viewed as quantized excitations of their respective fields. For example, the photon is associated with the electromagnetic field. While the photon itself is massless, it still carries energy, momentum, and other physical properties associated with its field. In a sense, you can think of a massless particle like a wave or vibration of its underlying field, rather than being composed of other particles with mass.
It's worth noting that our understanding of mass and the origin of particle masses is an active area of research in physics. The discovery of the Higgs boson at the Large Hadron Collider in 2012 was a significant step in our understanding of how particles acquire mass, but there is still ongoing exploration to deepen our understanding of this fundamental aspect of the universe.