String Theory Demystified

8 String Theory Demystifi ed
then I in Eq. (1.8) is fi nite and calculations give answers that make sense. On the
other hand, if the momentum p → but
λ > 0
the integral in Eq. (1.8) diverges. This leads to infi nities in calculations. Now if
I → but does so slowly, then a mathematical technique called renormalization
can be used to get fi nite results from calculations. Such is the case when working
with established theories like quantum electrodynamics.
The Standard Model
In its fi nished form, the theoretical framework that describes known particle
interactions with quantum fi eld theory is called the standard model. In the standard
model, there are three basic types of particle interactions. These are
• Electromagnetic
• Weak
• Strong (nuclear)
There are two basic types of particles in the standard model. These are
• Spin-1 gauge bosons that transmit particle interactions (they “carry” the
force). These include the photon (electromagnetic interactions), W ± and Z
(weak interactions), and gluons (strong interactions).
• Matter is made out of spin-1/2 fermions, such as electrons.
In addition, the standard model requires the introduction of a spin-0 particle called the
Higgs boson. Particles interact with the associated Higgs fi eld, and this interaction
gives particles their mass.
Quantizing the Gravitational Field
The general theory of relativity includes gravitational waves. They carry angular
momentum J = 2, so we deduce that the quantum of the gravitational fi eld, known
as the graviton, is a spin-2 particle. It turns out that string theory naturally includes