arXiv subjects

Marc Chemtob

Publications and source records attributed to Marc Chemtob.

14 recordsLinked to original sources

arXiv2024

Meson modes of probe $D7$-branes in Klebanov-Strassler background

We examine the properties of 4-d bosonic and fermionic (mesons and mesinos) modes on $D7$-branes wrapped over Kuperstein 4-cycle of the Klebanov-Strassler background. The wave equations are derived in a convenient parameterization of the warped deformed conifold metric. The mass spectra, wave functions and couplings of bosonic modes are evaluated by means of semi-classical tools. We explore the possible existence of fermionic zero modes.

hep-th↗

arXiv2022

Kaluza-Klein theory for type $II \ b$ supergravity on the warped deformed conifold

We discuss Kaluza-Klein theory for type $II\ b $ supergravity on the warped deformed conifold using a large radial distance limit of Klebanov-Strassler solution where the radial coordinate separates from angle coordinates for a background asymptotic to $ AdS _5 \times T^{1,1}$ spacetime. The decomposition of field fluctuations on harmonics of the base manifold $T^{1,1}$ and plane waves of $M_4= ð(AdS _5 )$ is examined for the metric tensor components along $M_4= ð(AdS _5 )$, the axio-dilaton and the 4-form potential components along $T^{1,1}$. Semi-classical methods are used to compute the mass spectra, wave functions and interactions for a set of modes in low dimensional representations of the isometry group. Deformations of the background solution due to compactification effects are also considered. The information on warped modes properties is utilized to explore the thermal evolution of a cosmic component of metastable modes after exit from brane inflation.

hep-th↗

arXiv2019

Warped modes in flux compactification of type II b supergravity on the conifold

We examine the Kaluza-Klein theory for warped flux compactifications of type $II\ b $ string theory on a Minkowski spacetime $ M_4$ times a conic Calabi-Yau orientifold $X_6$. The region glued along the internal space directions to the bulk of $X_6$ is modeled by the warped undeformed conifold $\calc _6$. The resulting classical vacum solution of Klebanov-Tseytlin solution, valid at large radial distances from the conic singularity, describes a spacetime asymptotic to $ AdS_5 $ times the conifold compact base $ T^{1,1}$. The metric tensor, axio-dilaton and antisymmetric fields part of the 10-d supergravity multiplet bosonic sector decompose into towers of scalar and tensor fields of fixed mass associated to harmonic modes of $T^{1,1}$ and $M_4$. The warped throat deformations by compactification effects are described by means of AdS/CFT duality. The applications are developed within the hard wall approximation for a truncated $ AdS_5 $ spacetime ending on flat boundaries. Numerical results are presented for the mass spectra and interactions of a selected set of singlet and charged modes and for the interactions of graviton modes with embedded branes. We examine the possibility that an interacting gas of warped massive modes produced after brane-antibrane inflation might reheat the universe and leave cold dark matter relics.

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arXiv2010

Searching singlet extensions of the supersymmetric standard model in $ Z_{6-II}$ orbifold compactification of heterotic string

We search for supersymmetric standard model realizations with extra singlets and extra $ U(1)$ using the heterotic string compactification on the $ Z_{6-II}$ orbifold with two Wilson lines. We analyze the vacuum restabilization mechanism for three representative Pati-Salam string models obtained in the literature and present detailed results for the effective superpotential compatible with the string selection rules. An automated selection of semi-realistic vacua along flat directions in the non-Abelian singlet modes field space is performed by requiring the presence of massless pairs of electroweak Higgs bosons having trilinear superpotential couplings with massless singlet modes and the decoupling of color triplet exotic modes needed to suppress $B $ and $ L $ number violating processes.

hep-ph↗

arXiv2008

Contact interactions in low scale string models with intersecting $D6$-branes

We evaluate the tree level four fermion string amplitudes in the TeV string mass scale models with intersecting $D6$-branes. The coefficient functions of contact interactions subsuming the contributions of string Regge resonance and winding mode excitations are obtained by subtracting out the contributions from the string massless and massive momentum modes. Numerical applications are developed for the Standard Model like solution of Cremades, Ibanez, and Marchesano for a toroidal orientifold with four intersecting $D6$-brane stacks. The chirality conserving contact interactions of the quarks and leptons are considered in applications to high energy collider and flavor changing neutral current phenomenology. The two main free parameters consist of the string and compactification mass scales, $ m_s$ and $ M_c$. Useful constraints on these parameters are derived from predictions for the Bhabha scattering differential cross section and for the observables associated to the mass shifts of the neutral meson systems $ K-\bar K, B-\bar B, D-\bar D$ and the lepton number violating three-body leptonic decays of the charged leptons $μ$ and $ τ$.

hep-ph↗

arXiv2007

Nucleon decay in gauge unified models with intersecting D6-branes

Baryon number violation is discussed in gauge unified orbifold models of type II string theory with intersecting Dirichlet branes. We consider setups of D6-branes which extend along the flat Minkowski space-time directions and wrap around 3-cycles of the internal 6-d manifold. The discussion is motivated by the enhancement effect of low energy amplitudes anticipated for M-theory and type II string theory models with matter modes localized at points of the internal manifold. The conformal field theory formalism is used to evaluate the open string amplitudes at tree level. We study the single baryon number violating processes of dimension 6 and 5, involving four quarks and leptons and in supersymmetry models, two pairs of matter fermions and superpartner sfermions. The higher order processes associated with the baryon number violating operators of dimension 7 and 9 are also examined, but in a qualitative way. We discuss the low energy representation of string theory amplitudes in terms of infinite series of poles associated to exchange of string Regge resonance and compactification modes. The comparison of string amplitudes with the equivalent field theory amplitudes is first studied in the large compactification radius limit. Proceeding next to the finite compactification radius case, we present a numerical study of the ratio of string to field theory amplitudes based on semi-realistic gauge unified non-supersymmetric and supersymmetric models employing the Z3 and Z2xZ2 orbifolds. We find a moderate enhancement of string amplitudes which becomes manifest in the regime where the gauge symmetry breaking mass parameter exceeds the compactification mass parameter, corresponding to a gauge unification in a seven dimensional space-time.

hep-ph↗

arXiv2004

Phenomenological constraints on broken R parity symmetry in supersymmetry models

The R parity odd renormalizable Yukawa interactions of quarks and leptons with the scalar superpartners have the ability to violate the baryon and lepton numbers, change the hadron and lepton flavors and make the lightest supersymmetric particle unstable. The existence of an approximate R parity symmetry would thus affect in a deep way the conventional framework of the Minimal Supersymmetric Standard Model where an exact R parity symmetry is built-in by assumption. The purpose of the present review is to survey in a systematic way the direct experimental constraints set on the R parity violating couplings by the low and intermediate energy physics processes. We consider first the option of bilinear R parity violation and spontaneously broken R parity symmetry and proceed next to the trilinear R parity violating interactions. The discussion aims at surveying the indirect coupling constant bounds derived from fundamental tests of the Standard Model and the variety of scattering and rare decay processes. We also discuss the constraints imposed by the renormalization group scale evolution and the cosmological and astrophysical phenomenology.

hep-ph↗

arXiv2000

Polarized Single Top Production at Leptonic Colliders from Broken R Parity Interactions Incorporating CP Violation

The contribution from the R parity violating interactions in the associated production of a top quark with a charm antiquark is examined for high energy leptonic colliders. We concentrate on the reactions associated with the semileptonic top decay. A set of characteristic dynamical distributions for the signal events is evaluated and the results contrasted against those from the standard model W-boson pair production background. Next, we turn to a study of a CP-odd observable, associated with the top spin, which leads to an asymmetry in the energy distribution of the emitted charged leptons for the pair of CP-conjugate final states, $b \bar l ν\bar c$ and $ \bar b l \bar νc $. A non vanishing asymmetry arises from a CP-odd phase, embedded in the R parity violating coupling constants, through interference terms between the R parity violating amplitudes at both the tree and loop levels.

hep-ph↗

arXiv1999

R-Parity Violating Contributions to Flavor Changing and CP Violation Effects in Fermion and Sfermion Pair Production

We examine the contributions from the R-parity odd interactions, $ ł_{ijk} L_iL_jE_k^c $ and $ ł'_{ijk} L_i Q_j D^c_k$, to the total rates and the CP asymmetry rates in the production of fermion-antifermion (lepton, down and up quark) pairs and slepton-antislepton pairs of different flavors at leptonic colliders. For the top-charm associated production case, we evaluate dynamical distributions for the semileptonic top decay events and estimate the sensitivity reach on the relevant parameters.

hep-ph↗

arXiv1998

Broken R Parity Contributions to Flavor Changing Rates and CP Asymmetries in Fermion Pair Production at Leptonic Colliders

We examine the effects of the R parity odd renormalizable interactions on flavor changing rates and CP violation asymmetries in the production of fermion-antifermion pairs at $e^-- e^+$ leptonic colliders. The produced fermions may be leptons, down-quarks or up-quarks, and the center of mass energies may range from the Z-boson pole up to $ 1000$ GeV. Off the Z-boson pole, the flavor changing rates are controlled by tree level amplitudes and the CP asymmetries by interference terms between tree and loop level amplitudes. At the Z-boson pole, both observables involve loop amplitudes. The lepton number violating interactions, associated with the coupling constants, $ł_{ijk}, ł'_{ijk}$, are only taken into account. The consideration of loop amplitudes is restricted to the photon and Z-boson vertex corrections. We briefly review flavor violation physics at colliders. We present numerical results using a single, species and family independent, mass parameter, $\tilde m$, for all the scalar superpartners and considering simple assumptions for the family dependence of the R parity odd coupling constants.

hep-ph↗

arXiv1998

Systematics of single superpartners production at leptonic colliders

We examine the effects of the lepton number violating R parity odd interactions, $λ_{ijk} $, on single production of fermion (charginos and neutralinos) and scalar (sleptons and sneutrinos) superpartners at leptonic colliders for center of mass energies up to $500GeV - 1TeV$. The probability amplitudes for all the five relevant $2 \to 2$ body processes and the decays branching ratios for the produced superpartners are calculated at tree level. A semi-quantitative discussion is developed within a supergravity model assuming grand unification of gauge interactions and universal (flavor independent) soft supersymmetry breaking parameters at the unification scale. The predictions obtained for the total and partial rates show that the single production reactions have a good potential of observability at NLC (Next Linear Colliders) energies. For values of the R parity violating coupling constant, $λ_{ijk}= 0.05$, close to the current bounds, the $\tilde χ^{\pm, 0}$ reactions could probe all the relevant intervals for $\tan β$ and $m_0$ and broad regions of the parameter space for $μ$ and $M_2$, while the $\tilde ν$ and $\tilde l $ productions could probe sneutrinos and sleptons masses up to the kinematical limits. Using the hypothesis of a single dominant R parity violating coupling constant, a Monte Carlo events simulation for the $ \tilde χ^{\pm, 0} $ reactions is employed to deduce some characteristic final states dynamical distributions.

hep-ph↗

arXiv1998

CP violation flavor asymmetries in slepton pair production at leptonic colliders from broken R parity

We examine the effect of the R parity odd renormalizable interactions on flavor non-diagonal rates and CP violation asymmetries in the production of slepton pairs at $e^- - e^+$ leptonic colliders, for center of mass energies spanning the interval from the Z-boson pole up to 1000 GeV. The lepton number violating interactions, associated with the lepton number violating coupling constants, are assumed to incorporate CP odd complex phases. The flavor changing rates are controlled by tree level amplitudes and quadratic products of different R parity violating coupling constants and the CP asymmetries by interference terms between tree and loop level amplitudes and quartic products. The consideration of loop amplitudes is restricted to the photon and Z-boson vertex corrections. We present numerical results using a family and species independent mass parameter, $\tilde m$, for all the scalar superpartners and making simple assumptions for the family dependence of the R parity odd coupling constants. The flavor non-diagonal rates, $\s_{JJ'}$, vary in the range, $(ł/0.1)^4 2 - 20$ fbarns, as one spans the interval of center of mass energies from the Z-boson pole up to 1000 GeV. For sleptons masses, $\tilde m> 150 $ GeV, these observables could be of use at NLC energies to set useful bounds on the R parity odd coupling constants. The values of the asymmetries, vary from a few to a few tens of $10^{-3}$.

hep-ph↗

arXiv1997

Systematics of string loop threshold corrections in orbifold models

String theory one-loop threshold corrections are studied in a background field approach due to Kiritsis and Kounnas which uses space-time curvature as an infrared regulator. We review the conformal field theory aspects using the semiwormhole space-time solution. The comparison of string and effective field theories vacuum functionals is made for the low derivative order, as well as for certain higher-derivative, gauge and gravitational interactions. We study the dependence on the infrared cut-off. Numerical applications are considered for a sample of four-dimensional abelian orbifold models. The implications on the perturbative string theory unification are examined. We present numerical results for the gauge interactions coupling constants as well as for the quadratic order gravitational ($R^2$) and the quartic order gauge ($F^4$) interactions.

hep-th↗

arXiv1995

Chiral symmetry breaking in strongly coupled scalar QED

Scalar QED with fermions is investigated in an expansion in powers of the inverse gauge coupling constant. The fermion mass generation is studied in next to leading order of the strong coupling expansion for the Higgs-phase of the model. Chiral symmetry breaking is discussed. Our approach supports from a strong coupling point of view the results obtained earlier by Miransky, Bardeen and Kondo.

hep-ph↗