Herman Verlinde's Homepage

My Research

My research field is string theory. Via the basic premise that elementary particles are tiny vibrating strings, that interact via joining and splitting, it aspires to furnish a unified description of all known fundamental forces, including gravity.

Strings can be closed or open. Closed strings are free to move in nine dimensions, of which six are compact, whereas their open counterparts attach to planes known as D-branes. Open strings naturally behave as matter particles, such as quarks, electrons, or vector bosons, while closed strings mediate gravity. The challenge of string phenomenology is to combine these ingredients into a consistent and predictive description of Nature.

String theory research has several branches. In the past ten years, much has been learned abouts its formal structure, its duality symmetries, and its space of solutions. In parallel, important new insights were obtained in the application of string theory to gauge theory, black hole physics and cosmology. A short summary of these advancements, and of my own work in these directions, is found here.

At present, particle physicists are eagerly awaiting the LHC experiment at Cern, which hopefully will discover exciting new physics beyond the Standard Model. Clearly, given its stated ambition, string theory must show its hand by the time LHC announces its first results. In the next few years, string phenomenology will again need to take center stage.

In recent work with Martijn Wijnholt, we have begun to develop a new "bottom-up" approach to string phenomenology, that aims to directly construct the Standard Model in terms of open strings attached to a D3-brane. The D3-brane fills space-time, but is just a single point within the six extra dimensions. The advantage of this set-up is that the spectrum and interactions of the particles that live on the D3-brane depend only on the local shape of the extra dimensions near this point. The challenge then is to find the correct local geometry that gives the Standard Model. In our recent paper we identify a promising candidate, that comes remarkably close to achieving this goal.

This set-up also provides a compelling geometric implementation of the gauge hierarchy, the large disparity between the Planck and electro-weak scale. A natural location for the D3-brane, namely, is at the apex of a highly warped, cone-like region. The cone forms an exponentially deep gravitational well, trapping all sub-Planck scale physics near its tip.

Via this bottom-up approach, the task of string phenomenology gets divided into two steps. First one constructs the correct geometry near the tip of the cone, such that the open strings on the D3-brane reproduce the Standard Model. Then as the second step, one looks for a suitable compact geometry that can be used to cap off the cone. This procedure can be thought of as constructing the UV completion of the theory, with consistent Planck scale dynamics. Completing both steps is a highly non-trivial task, but we view this as a promising route towards the ultimate goal of connecting string theory with experiment.