Sergei Dubovsky

Astrophysical probes of unification

Traditional ideas for testing unification involve searching for the decay of the proton and its branching modes. We point out that several astrophysical experiments are now reaching sensitivities that allow them to explore supersymmetric unified theories. In these theories the electroweak-mass dark matter particle can decay, just like the proton, through dimension 6 operators with lifetime {approx}10{sup 26} s. Interestingly, this time scale is now being investigated in several experiments including ATIC, PAMELA, HESS, and Fermi. Positive evidence for such decays may be opening our first direct window to physics at the supersymmetric unification scale of M{sub GUT}{approx}10{sup 16} GeV, as well as the TeV scale. Moreover, in the same supersymmetric unified theories, dimension 5 operators can lead a weak-scale superparticle to decay with a lifetime of {approx}100 s. Such decays are recorded by a change in the primordial light element abundances and may well explain the present discord between the measured Li abundances and standard big bang nucleosynthesis, opening another window to unification. These theories make concrete predictions for the spectrum and signatures at the LHC as well as Fermi.

Effective String Theory Revisited

A bstractWe revisit the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.

Solving the simplest theory of quantum gravity

A bstractWe solve what is quite likely the simplest model of quantum gravity, the worldsheet theory of an infinitely long, free bosonic string in Minkowski space. Contrary to naive expectations, this theory is non-trivial. We illustrate this by constructing its exact factorizable S-matrix. Despite its simplicity, the theory exhibits many of the salient features expected from more mature quantum gravity models, including the absence of local off-shell observables, a minimal length, as well as (integrable relatives of) black holes. All these properties follow from the exact S-matrix. We show that the complete finite volume spectrum can be reconstructed analytically from this S-matrix with the help of the thermodynamic Bethe Ansatz. We argue that considered as a UV complete relativistic 2-dimensional quantum field theory the model exhibits a new type of renormalization group flow behavior, “asymptotic fragility”. Asymptotically fragile flows do not originate from a UV fixed point.

Decaying Dark Matter As a Probe of Unification And TeV Spectroscopy

In supersymmetric unified theories the dark matter particle can decay, just like the proton, through grand unified interactions with a lifetime of order of

Natural tuning: towards a proof of concept

\ensuremath{\sim}{10}^{26}\text{ }\text{ }\mathrm{sec}

Axion monodromy in a model of holographic gluodynamics

. Its decay products can be detected by several experiments\char22{}including Fermi, HESS, PAMELA, ATIC, and IceCube\char22{}opening our first direct window to physics at the TeV scale and simultaneously at the unification scale

Flux Tube Spectra from Approximate Integrability at Low Energies

\ensuremath{\sim}{10}^{16}\text{ }\text{ }\mathrm{GeV}

Towards a Theory of the QCD String

. We consider possibilities for explaining the electron/positron spectra observed by HESS, PAMELA, and ATIC, and the resulting predictions for the gamma-ray, electron/positron, and neutrino spectra as will be measured, for example, by Fermi and IceCube. The discovery of an isotropic, hard gamma ray spectral feature at Fermi would be strong evidence for dark matter and would disfavor astrophysical sources such as pulsars. Substructure in the cosmic ray spectra probes the spectroscopy of new TeV-mass particles. For example, a preponderance of electrons in the final state can result from the lightness of selectrons relative to squarks. Decaying dark matter acts as a sparticle injector with an energy reach potentially higher than the LHC. The resulting cosmic ray flux depends only on the values of the weak and unification scales.

The volume of the universe after inflation and de Sitter entropy

A bstractThe cosmological constant problem and the absence of new natural physics at the electroweak scale, if confirmed by the LHC, may either indicate that the nature is fine-tuned or that a refined notion of naturalness is required. We construct a family of toy UV complete quantum theories providing a proof of concept for the second possibility. Low energy physics is described by a tuned effective field theory, which exhibits relevant interactions not protected by any symmetries and separated by an arbitrary large mass gap from the new “gravitational” physics, represented by a set of irrelevant operators. Nevertheless, the only available language to describe dynamics at all energy scales does not require any fine-tuning. The interesting novel feature of this construction is that UV physics is not described by a fixed point, but rather exhibits asymptotic fragility. Observation of additional unprotected scalars at the LHC would be a smoking gun for this scenario. Natural tuning also favors TeV scale unification.

Asymptotic fragility, near AdS2 holography and TT¯

A bstractThe low energy field theory for N type IIA D4-branes at strong ’t Hooft coupling, wrapped on a circle with antiperiodic boundary conditions for fermions, is known to have a vacuum energy which depends on the θ angle for the gauge fields, and which is a multivalued function of this angle. This gives a field-theoretic realization of “axion monodromy” for a nondynamical axion. We construct the supergravity solution dual to the field theory in the metastable state which is the adiabatic continuation of the vacuum to large values of θ. We compute the energy of this state and show that it initially rises quadratically and then flattens out. We show that the glueball mass decreases with θ, becoming much lower than the 5d KK scale governing the UV completion of this model. We construct two different classes of domain walls interpolating between adjacent vacua. We identify a number of instability modes — nucleation of domain walls, bulk Casimir forces, and condensation of tachyonic winding modes in the bulk — which indicate that the metastable branch eventually becomes unstable. Finally, we discuss two phenomena which can arise when the axion is dynamical; axion-driven inflation, and axion strings.