Searcharxiv⌕ Search

arXiv subjects

S. L. Dubovsky

Publications and source records attributed to S. L. Dubovsky.

33 records · Page 2Linked to original sources
arXiv2000

Statistics of clustering of ultra-high energy cosmic rays and the number of their sources

Observation of clustering of ultra-high energy cosmic rays (UHECR) suggests that they are emitted by compact sources. Assuming small deflection of UHECR during the propagation, the statistical analysis of clustering allows to estimate the spatial density of the sources, h, including those which have not yet been observed directly. When applied to astrophysical models involving extra-galactic sources, the estimate based on 14 events with energy E>10^{20} eV gives h ~ 6 X 10^{-3} Mps^{-3}. With increasing statistics, this estimate may lead to exclusion of the models which associate the production of UHECR with exceptional galaxies such as AGN, powerful radio-galaxies, dead quasars, and models based on gamma ray bursts.

astro-ph↗
arXiv2000

Brane world: disappearing massive matter

In a brane (domain wall) scenario with an infinite extra dimension and localized gravity, bulk fermions and scalars often have bound states with zero 4-dimensional mass. In this way massless matter residing on the brane may be obtained. We consider what happens when one tries to introduce small, but non-vanishing mass to these matter fields. We find that the discrete zero modes turn into quasi-localized states with finite 4-dimensional mass and finite width. The latter is due to tunneling of massive matter into extra dimension. We argue that this phenomenon is generic to fields that can have bulk modes. We also point out that in theories meant to describe massive scalars, the 4-dimensional scalar potential has, in fact, power-law behavior at large distances.

hep-th↗
arXiv2000

Induced charge matching and Wess-Zumino term on quantum modified moduli space

Recently it was proposed that matching of global charges induced in vacuum by slowly varying, topologically non-trivial scalar fields provides consistency conditions analogous to the 't Hooft anomaly matching conditions. We study matching of induced charges in supersymmetric SU(N) gauge theories with quantum modified moduli space. We find that the Wess-Zumino term should be present in the low energy theory in order that these consistency conditions are satisfied. We calculate the lowest homotopy groups of the quantum moduli space, and show that there are no obstructions to the existence of the Wess-Zumino term at arbitrary N. The explicit expression for this term is given. It is shown that neither vortices nor topological solitons exist in the model. The case of softly broken supersymmetry is considered as well. We find that the possibility of global flavor symmetric vacuum is strongly disfavored.

hep-th↗
arXiv2000

Orbifold projection in supersymmetric QCD at N_f\leq N_c

Supersymmetric orbifold projection of N=1 SQCD with relatively small number of flavors (not larger than the number of colors) is considered. The purpose is to check whether orbifolding commutes with the infrared limit. On the one hand, one considers the orbifold projection of SQCD and obtains the low-energy description of the resulting theory. On the other hand, one starts with the low-energy effective theory of the original SQCD, and only then perfoms orbifolding. It is shown that at finite N_c the two low-energy theories obtained in these ways are different. However, in the case of stabilized run-away vacuum these two theories are shown to coincide in the large N_c limit. In the case of quantum modified moduli space, topological solitons carrying baryonic charges are present in the orbifolded low-energy theory. These solitons may restore the correspondence between the two theories provided that the soliton mass tends to zero in the large N_c limit.

hep-th↗
arXiv1999

Generation of 10^15 - 10^17 eV photons by UHE CR in the Galactic magnetic filed

We show that the deep expected in the diffuse photon spectrum above the threshold of e+e- pair production, i.e., at energies 10^15 - 10^17 eV, may be absent due to the synchrotron radiation by the electron component of the extragalactic Ultra-High Energy Cosmic Rays (UHE CR) in the Galactic magnetic filed. The mechanism we propose requires small (less than 2x10^-12 G) extragalactic magnetic fields and large fraction of photons in the UHE CR. For a typical photon flux expected in top-down scenarios of UHE CR, the predicted flux in the region of the deep is close to the existing experimental limit. The sensitivity of our mechanism to the extragalactic magnetic field may be used to improve existing bounds on the latter by two orders of magnitude.

astro-ph↗
arXiv1999

Gauge mechanism of mediation of supersymmetry breaking

Most phenomenologically acceptable supersymmetric models imply breaking of supersymmetry in a separate sector of fields introduced just for this purpose. Supersymmetry breaking is transferred to the Standard Model due to a certain interaction with this additional sector. In this review we disuss one of the popular mechanisms of such mediation with the key role played by the Standard Model gauge interactions. We consider general principles of gauge mediation and give the critical analysis of specific models together with their phenomenological and cosmological implications. We present also basic facts concerning mechanisms of dynamical supersymmetry breaking.

hep-ph↗
arXiv1999

Flavor violation and $\tanβ$ in gauge mediated models with messenger-matter mixing

We consider the Minimal Gauge Mediated Model (MGMM) with either fundamental or antisymmetric messenger multiplets and study consequences of messenger-matter mixing. We find that in these models, unlike MGMM without mixing, wide range of $\tanβ$ is allowed. It is shown that existing experimental limits on processes with lepton flavor violation, and on $K^0-\bar{K}^0$, $D^0-\bar{D}^0$ and $B^0-\bar{B}^0$ - mixing place significant constraints on relevant coupling constants and mixing parameters. On the other hand, the contributions of the messenger-matter mixing to the rates of $τ\to eγ$, $τ\to μγ$ and $b\to sγ$ may be well below the present experimental limits depending on the value of $\tanβ$. We also point out the possibility of sizeable slepton oscillations in this model.

hep-ph↗
arXiv1999

Non-renormalization of induced charges and constraints on strongly coupled theories

It is shown that global fermionic charges induced in vacuum by slowly varying, topologically non-trivial background scalar fields are not renormalized provided that expansion in momenta of background fields is valid. This suggests that strongly coupled theories obey induced charge matching conditions which are analogous, but generally not equivalent, to 't Hooft anomaly matching conditions. We give a few examples of induced charge matching. In particular, the corresponding constraints in softly broken supersymmetric QCD suggest non-trivial low energy mass pattern, in full accord with the results of direct analyses.

hep-th↗
arXiv1998

Galactic anisotropy of Ultra-High Energy Cosmic Rays produced by CDM-related mechanisms

We briefly review current theoretical and experimental status of Ultra-High Energy Cosmic Rays. We show that ``top-down'' mechanisms of UHE CR which involve heavy relic particle-like objects predict Galactic anisotropy of highest energy cosmic rays at the level of minimum $\sim 20%$. This anisotropy is large enough to be either observed or ruled out in the next generation of experiments.

hep-ph↗
arXiv1998

Low $\tanβ$ in the extended Minimal Gauge Mediated Model

We consider the Minimal Gauge Mediated Model (MGMM) with either fundamental or antisymmetric messenger multiplets and study consequences of messenger-matter mixing. It is shown that constraints on relevant coupling constants and mixing parameters coming from the existing experimental limits on lepton flavor violation and FCNC processes allow a wide range of $\tanβ$ in MGMM with mixing.

hep-ph↗
arXiv1998

Grand unification with gauge mediated supersymmetry breaking

We consider constraints on gauge mediated supersymmetry breaking models imposed by the requirement of grand unification. In particular, we demonstrate several ways to reduce the number of parameters coming from the dynamical supersymmetry breaking sector. One of approaches exploits nonperturbative unification of gauge couplings in multi-messenger models.

hep-ph↗
arXiv1998

Dynamical supersymmetry breaking and unification of couplings

We consider the possibility of unification of the Supersymmetric Standard Model gauge groups with those of the dynamical supersymmetry breaking (DSB) sector in theories with gauge mediated supersymmetry breaking. We find constraints on the DSB gauge group beta function that come from unification of the gauge coupling constants of the two sectors. These constraints are satisfied by a fairly wide class of models. We discuss possible unification scenarios in the context of a simple model.

hep-ph↗
arXiv1998

Towards common origin of supersymmetry breaking, compositeness, and gauge mediation

We present a toy model which has the following properties: i) it is strongly coupled at a certain scale and breaks supersymmetry at this scale; ii) matter superfields of (one generation of) the Standard Model are effective low energy degrees of freedom of this strongly coupled theory; iii) direct gauge mediation of supersymmetry breaking occurs due to messenger superfields that are also effective low energy degrees of freedom. We discuss the way to generalize this approach to realistic models with three generations. These models might be favorable from the point of view of string theory compactifications.

hep-ph↗
arXiv1997

Messenger-matter mixing and lepton flavor violation

We consider the Minimal Gauge Mediated Model (MGMM) with messenger-matter mixing and find that existing experimental limits on $μ\to eγ$ decay and $μ- e$ - conversion place significant constraints on relevant coupling constants. On the other hand, the rates of $τ\to eγ$ and $τ\to μγ$ in MGMM are well below the existing limits. We also point out the possibility of sizeable slepton oscillations in this model.

hep-ph↗