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D. S. Gorbunov

Publications and source records attributed to D. S. Gorbunov.

72 records · Page 4Linked to original sources
arXiv2001

Kaon Physics with Light Sgoldstinos and Parity Conservation

Superpartners of goldstino -- scalar and pseudoscalar sgoldstinos -- interact weakly with ordinary particles. One or both of them may be light. We consider a class of supersymmetric extensions of the Standard Model in which interactions of sgoldstinos with quarks and gluons conserve parity but do not conserve quark flavor. If the pseudoscalar sgoldstino $P$ is light, m_P<(m_K-2m_π), and the scalar sgoldstino is heavier, m_S>(m_K-m_π), an interesting place for experimental searches is the poorly explored area of three-body decays of kaons, K^0_{S,L}\toπ^+π^- P, K^0_{S,L}\toπ^0π^0 P and K^+\toπ^+π^0 P, with $P$ subsequently decaying into γγ, possibly e^+e^-, or flying away from the detector. We evaluate the constraints on the flavor-violating coupling of sgoldstino to quarks which are imposed by K^0_L-K^0_S mass difference and CP-violation in neutral kaon system, and find that these constraints allow for fairly large Br(K\toππP). We find that the most interesting ranges of branching ratios start at Br(K^0_L\toππP)\sim 10^{-3}, Br(K^+\toπ^+π^0 P)\sim 10^{-4}, Br(K_S^0\toππP)\sim 10^{-3}. These searches for light pseudoscalar sgoldstino would be sensitive to the supersymmetry breaking scale \sqrt{F} in the 100 TeV range and above. We also briefly discuss the cases of light scalar sgoldstino and relatively heavy sgoldstinos.

hep-ph↗
arXiv2001

Gravity waves from inflating brane or Mirrors moving in adS$_5$

We study tensor perturbations in a model with inflating Randall--Sundrum-type brane embedded in five-dimensional anti-de Sitter (adS$_5$) bulk. In this model, a natural {\it in}-vacuum of gravitons is the vacuum defined in static adS$_5$ frame. We show that this vacuum is, in fact, the same as the {\it in}-vacuum defined in the frame with de Sitter (dS$_4$) slicing, in which the brane is at rest. Thus, during inflation, gravitons on and off the brane remain in their vacuum state. We then study graviton creation by the brane on which inflation terminates at some moment of time. We mostly consider gravitons whose wavelengths at the end of inflation exceed both the horizon size and the adS$_5$ radius. Creation of these gravitons is dominated by (zero mode)--(zero mode) Bogoliubov coefficients and, apart from an overall factor, the spectrum of produced gravitons is the same as in four-dimensional theory. ``Kaluza--Klein'' gravitons are also produced, but this effect is subdominant. Graviton spectra at somewhat higher momenta are also presented for completeness.

hep-th↗
arXiv2001

Light Sgoldstino: Precision Measurements versus Collider Searches

We study sensitivity of low-energy experiments to the scale of supersymmetry breaking $\sqrt{F}$ in models with light sgoldstinos --- superpartners of goldstino. The limits on $\sqrt{F}$ may be obtained from direct and indirect measurements of sgoldstino coupling to photons, leptons, mesons and nucleons. There are three sources of constraints: ($i$) astrophysics and cosmology; ($ii$) precision laboratory experiments at low energies; ($iii$) rare decays. We discuss only processes with real sgoldstinos. For sgoldstino lighter than a few MeV and superpartner masses of the order of electroweak scale, astrophysical and reactor bounds on $\sqrt{F}$ are significantly stronger than limits which may be reached at future colliders. In models with heavier sgoldstino (up to 5 GeV), constraints from flavor conserving decays of mesons are complementary to ones coming from collider experiments. The most sensitive probes of sgoldstinos are flavor violating processes, provided that flavor is violated in squark and/or slepton sector. It is shown that sgoldstino contributions into FCNC and lepton flavor violation are strong enough to probe the supersymmetry breaking scale up to $\sqrt{F}\sim10^7$ GeV, if off-diagonal entries in squark (slepton) mass matrices are close to the current limits in MSSM.

hep-ph↗
arXiv2001

Axion-like particles as ultra high energy cosmic rays?

If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from BL Lacertae at cosmological distances as suggested by recent studies, the absence of the GZK cutoff can not be reconciled with Standard-Model particle properties. Axions would escape the GZK cutoff, but even the coherent conversion and back-conversion between photons and axions in large-scale magnetic fields is not enough to produce the required flux. However, one may construct models of other novel (pseudo)scalar neutral particles with properties that would allow for sufficient rates of particle production in the source and shower production in the atmosphere to explain the observations. As an explicit example for such particles we consider SUSY models with light sgoldstinos.

hep-ph↗
arXiv2001

Small Second Acoustic Peak from Interacting Cold Dark Matter?

We consider a possibility to explain the observed suppression of the second acoustic peak in the anisotropy spectrum of the Cosmic Microwave Background (CMB) by interaction between a fraction of non-baryonic Cold Dark Matter (CDM) and normal baryonic matter. This scenario does not require any modifications in the standard Big Bang Nucleosynthesis (BBN). We estimate the required values of the cross-section-to-mass ratio for elastic scattering of CDM particles off baryons. In case of velocity-independent elastic scattering (in the velocity interval 10^{-5}--10^{-3}) we find that such particles do not contradict observational limits if they are heavier than \sim 10^5 GeV or lighter than \sim 0.5 GeV. Another candidate, which may appear in the models with infinite extra dimensions, is a quasistable charged particle decaying through tunneling into extra dimensions. Finally a millicharged particle with the electric charge ranging from \sim 10^{-4} to \sim 10^{-1} and with mass M\sim 0.1 GeV--1 TeV also may be responsible for the suppression of the second acoustic peak. As a byproduct we point out that CMB measurements set new limits on the allowed parameter space for the millicharged particles.

astro-ph↗
arXiv2001

TESLA: Potentials of $γγ$ and $e^+e^-$ Options in Stoponium Searches

In some supersymmetric extensions of the Standard Model fairly light superpartner of t-quark is predicted, which may form bound states - stoponiums. We estimate potentials of TESLA linear collider in search for stoponium, considering the basic e+e- option and the gamma-gamma option (Photon Linear Collider - PLC). It is found that PLC could be the best machine for discovery of these new narrow strong resonances. It can produce thousands stoponiums per 100 fb$^-1$ integrated luminosity in the high energy peak. In the case of scenarios when stoponium decays mainly into gluons the signal/background ratio is about 1/4. The channel S->hh into two lightest Higgs bosons could be also seen with high significance. Thus, several weeks run is sufficient for the stoponium discovery, if its mass is approximately known (e.g. from observation of direct stops production at LHC). Then, in MSSM scenarios with dominant S->hh decay PLC shows excellent possibilities to discover bound state of stops, practically immediately after beginning of operating. The e+e- option also has some prospects to observe stoponium but only in the case of scenarios with dominant decay into two lightest Higgs bosons, with tens of events per 100 $fb^{-1}$. Interesting possibility appears in the case when the resonance is seated on 0.1% width luminosity peak - one could resolve the stoponium exited states.

hep-ph↗
arXiv2000

Stoponium Search at Photon Linear Collider

In some supersymmetric extensions of the Standard Model fairly light superpartner of t-quark is predicted, which may form bound states ({\it stoponiums}) under certain conditions. We study prospects of search for stoponium at the future Photon Linear Collider. It is found that this machine could be the best machine for discovery and study of these resonances at some scenarios of supersymmetric extension of the Standard Model. In particular, if the $hh$ decay channel is dominant stoponium could be observed at the beginning of PLC run with collision energy tuned at the stoponium mass. If this channel is kinematically closed stoponium could be discovered in $gg$, $γγ$ and $ZZ$ decay channels but higher statistics are needed. Effects of the stoponium-Higgs mixing and degeneracy are briefly discussed.

hep-ph↗
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

On Electroweak Baryogenesis in Gauge Mediated Models with Messenger-Matter Mixing

We consider feasibility of electroweak baryogenesis in gauge mediated supersymmetry breaking models with messenger-matter mixing. We present a class of models where electroweak baryogenesis produces sufficient amount of baryon asymmetry. The main features of these models are ({\it i}) large mixing between messengers and right stop and ({\it ii}) fairly narrow region of viable $\tanβ$.

hep-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

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↗