arXiv subjects
Publications and source records attributed to Sven Bjarke Gudnason.
We construct a D-brane soliton, a composite topological soliton sharing some properties with a D-brane, in a Skyrme model in 4+1 dimensions, in which Skyrmions are strings ending on a domain wall. We further generalize this D-brane soliton to diverse dimensions. A string, carrying the $π_{N-1}$ topological charge, ends on a domain wall in an O(N) model with higher-derivative terms in N+1 dimensions.
We study a Skyrme-type model with a potential term motivated by Bose-Einstein condensates (BECs), which we call the BEC Skyrme model. We consider two flavors of the model, the first is the Skyrme model and the second has a sixth-order derivative term instead of the Skyrme term; both with the added BEC-motivated potential. The model contains toroidally shaped Skyrmions and they are characterized by two integers P and Q, representing the winding numbers of two complex scalar fields along the toroidal and poloidal cycles of the torus, respectively. The baryon number is B=PQ. We find stable Skyrmion solutions for P=1,2,3,4,5 with Q=1, while for P=6 and Q=1 it is only metastable. We further find that configurations with higher Q>1 are all unstable and split into Q configurations with Q=1. Finally we discover a phase transition, possibly of first order, in the mass parameter of the potential under study.
We study local temperature fluctuations in a 2+1 dimensional CFT on the sphere, dual to a black hole in asymptotically AdS spacetime. The fluctuation spectrum is governed by the lowest-lying hydrodynamic modes of the system whose frequency and damping rate determine whether temperature fluctuations are thermal or quantum. We calculate numerically the corresponding quasinormal frequencies and match the result with the hydrodynamics of the dual CFT at large temperature. As a by-product of our analysis we determine the appropriate boundary conditions for calculating low-lying quasinormal modes for a four-dimensional Reissner-Nordström black hole in global AdS.
Skyrmions can be transformed into lumps or baby-Skyrmions by being trapped inside a domain wall. Here we find that they can also be transformed into sine-Gordon kinks when confined by vortices, resulting in confined Skyrmions. We show this both by an effective field theory approach and by direct numerical calculations. The existence of these trapped and confined Skyrmions does not rely on higher-derivative terms when the host solitons are flat or straight. We also construct a Skyrmion as a twisted vortex ring in a model with a sixth-order derivative term.
In the large flux limit vortices become flux tubes with almost constant magnetic field in the interior region. This occurs in the case of non-Abelian vortices as well, and the study of such configurations allows us to reveal a close relationship between vortex zero modes and the gyromagnetic instabilities of vector bosons in a strong background magnetic field discovered by Nielsen, Olesen and Ambjørn. The BPS vortices are exactly at the onset of this instability, and the dimension of their moduli space is precisely reproduced in this way. We present a unifying picture in which, through the study of the linear spectrum of scalars, fermions and W bosons in the magnetic field background, the expected number of translational, orientational, fermionic as well as semilocal zero modes is correctly reproduced in all cases.
Skyrmions of different dimensions are related by domain walls. We obtain explicit full numerical solutions of various Skyrmion configurations trapped inside a domain wall. We find for the quadratic mass-term that multi-Skyrmions are ring-shaped, and conjecture for the linear mass-term, that the lowest-energy state of multi-Skyrmions will consist of charge-2 rings accommodated in a lattice.
We construct a spherical domain wall which has baryon charge distributed on a sphere of finite radius in a Skyrme model with a sixth order derivative term and a modified mass term. Its distribution of energy density likewise takes the form of a sphere. In order to localize the domain wall at a finite radius we need a negative coefficient in front of the Skyrme term and a positive coefficient of the sixth order derivative term to stabilize the soliton. Increasing the pion mass pronounces the shell-like structure of the configuration.
We use the AdS/CFT correspondence to study a thermally isolated conformal field theory in four dimensions which undergoes a repeated deformation by an external periodic time-dependent source coupled to an operator of dimension Delta. The initial state of the theory is taken to be at a finite temperature. We compute the energy dissipated in the system as a function of the frequency and of the dimension Delta of the perturbing operator. This is done in the linear response regime. In order to study the details of thermalization in the dual field theory, the leading-order backreaction on the AdS black brane metric is computed. The evolution of the event and the apparent horizons is monitored; the increase of area in each cycle coincides with the increase in the equilibrium entropy corresponding to the amount of energy dissipated. The time evolution of the entanglement entropy of a spherical region and that of the two-points function of a probe operator with a large dimension are also inspected; we find a delay in the thermalization of these quantities which is proportional to the size of the region which is being probed. Thus, the delay is more pronounced in the infrared. We comment on a possible transition in the time evolution of the energy fluctuations.
In the framework of a gauge mediated quiver-like model, the standard model flavor texture can be naturally generated. The model - like the MSSM - has furthermore a region in parameter space where the lightest Higgs mass is fed by heavy stop loops, which in turn sets the average squark mass scale near 10-20 TeV. We perform a careful flavor analysis to check whether this type of mild-split SUSY passes all flavor constraints as easily as envisioned in the original type of split SUSY. Interestingly, it turns out to be on the border of several constraints, in particular, the branching ratio of mu -> e gamma and, if order one complex phases are assumed, also epsilon_K neutron and electron EDM. Furthermore, we consider unification as well as dark matter candidates, especially the gravitino. Finally, we provide a closed-form formula for the soft masses of matter in arbitrary representations of any of the gauge groups in a generic quiver-like model with a general messenger sector.
We construct meta-stable knotted domain strings on the surface of a soliton of the shape of a torus in 3+1 dimensions. We consider the simplest case of Z2 Wess-Zumino-type domain walls for which we can cover the torus with a domain string accompanied with an anti-domain string. In this theory, all (p,q)-torus knots can be realized as a linked pair of a(n) (un)knotted domain string and an anti-domain string.
The discovery of a SM-like Higgs boson near 125 GeV and the flavor texture of the Standard Model motivate the investigation of supersymmetric quiver-like BSM extensions. We study the properties of such a minimal class of models which deals naturally with the SM parameters. Considering experimental bounds as well as constraints from flavor physics and Electro-Weak Precision Data, we find the following. In a self-contained minimal model - including the full dynamics of the Higgs sector - top squarks below a TeV are in tension with b->sγ constraints. Relaxing the assumption concerning the mass generation of the heavy Higgses, we find that a stop not far from half a TeV is allowed. The models have some unique properties, e.g. an enhancement of the h-> b\bar{b},τ\bar{τ} decays relative to the h->γγ one, a gluino about 3 times heavier than the stop, an inverted hierarchy of about 3-20 between the squarks of the first two generations and the stop, relatively light Higgsino neutralino or stau NLSP, as well as heavy Higgses and a W' which may be within reach of the LHC.
We consider theories with time-dependent Hamiltonians which alternate between being bounded and unbounded from below. For appropriate frequencies dynamical stabilization can occur rendering the effective potential of the system stable. We first study a free field theory on a torus with a time-dependent mass term, finding that the stability regions are described in terms of the phase diagram of the Mathieu equation. Using number theory we have found a compactification scheme such as to avoid resonances for all momentum modes in the theory. We further consider the gravity dual of a conformal field theory on a sphere in three spacetime dimensions, deformed by a doubletrace operator. The gravity dual of the theory with a constant unbounded potential develops big crunch singularities; we study when such singularities can be cured by dynamical stabilization. We numerically solve the Einstein-scalar equations of motion in the case of a time-dependent doubletrace deformation and find that for sufficiently high frequencies the theory is dynamically stabilized and big crunches get screened by black hole horizons.
We propose a model of dark matter: galaxy-sized 't Hooft-Polyakov magnetic monopoles in a new, extraordinarily weakly coupled SU(2) gauge sector with an adjoint Higgs field and two flavors of fundamental fermions. We fit the parameters by asserting that the dark matter halos of the lightest dwarf spheroidal (dSph) galaxies consist of a single charge Q=1 monopole. Lensing and wide binary bounds are then easily satisfied and the monopoles form in time to help with CMB fluctuations. In this model dSph and low surface brightness (LSB) halos automatically have (1) A minimum mass - Dirac quantization solves the missing satellite problem, (2) A constant density core (r<r_1), (3) An intermediate regime (r_1<r<r_2) with density proportional to 1/r^2. The model predicts that (A) r_1 is proportional to the stellar rotational/dispersion velocities at r_1<r<r_2, (B) r_2 is reasonably Q independent and so dSph halos extend at least ten times farther than their half-light and tidal radii, (C) The minimal stellar dispersion is 1/sqrt{2} times the next-smallest allowed value. A serious potential problem with our proposal is that non-BPS monopoles are repulsive. The Jackiw-Rebbi mechanism yields four species of monopoles, and we assume that, for some choice of Yukawa couplings, one species is light and serves only to screen the repulsive interactions of another.
We present a class of supersymmetric models which address the flavor puzzle and have an inverted hierarchy of sfermions. Their construction involves quiver-like models with link fields in generic representations. The magnitude of Standard-Model parameters is obtained naturally and a relatively heavy Higgs boson is allowed without fine tuning. Collider signatures of such models are possibly within the reach of LHC in the near future.
It has been known for 30 years that 't Hooft-Polyakov monopoles of charge Q greater than one cannot be spherically symmetric. 5 years ago, Bolognesi conjectured that, at some point in their moduli space, BPS monopoles can become approximately spherically symmetric in the high Q limit. In this note we determine the sense in which this conjecture is correct. We consider an SU(2) gauge theory with an adjoint scalar field, and numerically find configurations with Q units of magnetic charge and a mass which is roughly linear in Q, for example in the case Q=81 we present a configuration whose energy exceeds the BPS bound by about 54 percent. These approximate solutions are constructed by gluing together Q cones, each of which contains a single unit of magnetic charge. In each cone, the energy is largest in the core, and so a constant energy density surface contains Q peaks and thus resembles a sea urchin. We comment on some relations between a non-BPS cousin of these solutions and the dark matter halos of dwarf spherical galaxies.
The soft masses due to SUSY breaking, mediated by gauge fields, are computed for generic matter in quiver gauge theories.
In direct gauge mediation, the gaugino masses are anomalously small, giving rise to a split SUSY spectrum. Here we investigate the superpartner spectrum in a minimal version of "direct gaugino mediation." We find that the sfermion masses are comparable to those of the gauginos - even in the hybrid gaugino-gauge mediation regime - if the messenger scale is sufficiently small.
Effects of mass deformations on 1/2 Bogomol'nyi-Prasad-Sommerfield (BPS) non-Abelian vortices are studied in 4d N=2 supersymmetric U(1) \times SO(2n) and U(1) \times USp(2n) gauge theories, with Nf=2n quark multiplets. The 2d N=(2,2) effective worldsheet sigma models on the Hermitian symmetric spaces SO(2n)/U(n) and USp(2n)/U(n) found recently which describe the low-energy excitations of the orientational moduli of the vortices, are generalized to the respective massive sigma models. The continuous vortex moduli spaces are replaced by a finite number (2^{n-1} or 2^{n}) of vortex solutions. The 1/2 BPS kinks connecting different vortex vacua are magnetic monopoles in the 4d theory, trapped inside the vortex core, with total configurations being 1/4 BPS composite states. These configurations are systematically studied within the semi-classical regime.