Borut Bajc

Jožef Stefan Institute | IJS · Theoretical Physics

We provide an example of an ultraviolet finite supersymmetric grand unified theory of safe rather than free nature endowed with a supersymmetric dynamical breaking mechanism. Our results simultaneously enlarge the number of ultraviolet consistent supersymmetric grand unified theories while providing a relevant example of how to achieve a consistent...

A bstract In the context of E 6 Grand Unified Theories (GUTs), an intriguing possibility for symmetry breaking to the Standard Model (SM) group involves an intermediate stage characterized by either SU(3) × SU(3) × SU(3) (trinification) or SU(6) × SU(2). The more common choices of SU(5) and SO(10) GUT symmetry groups do not offer such breaking chai...

In the context of $\mathrm{E}_{6}$ Grand Unified Theories (GUTs), an intriguing possibility for symmetry breaking to the Standard Model (SM) group involves an intermediate stage characterized by either $\mathrm{SU}(3)\times\mathrm{SU}(3)\times\mathrm{SU}(3)$ (trinification) or $\mathrm{SU}(6)\times\mathrm{SU}(2)$. The more common choices of $\mathr...

A bstract Using the AdS/CFT correspondence we model the behaviour of the two-point correlator of an operator with arbitrary scale dimension ∆ in arbitrary spacetime dimension d for small but non-zero temperature. The obtained propagator coincides in the low temperature regime with the known result for d = 4 for large ∆ at the order T d as well as w...

We investigate the high temperature fate of four-dimensional gauge-Yukawa theories featuring short distance conformality of either interacting or noninteracting nature. The latter is known as complete asymptotic freedom and, as templates, we consider non-Abelian gauge theories featuring either two singlet scalars coupled to gauged fermions via Yuka...

We investigate the high temperature fate of four dimensional gauge-Yukawa theories featuring short distance conformality of either interacting or non-interacting nature. The latter is known as complete asymptotic freedom and, as templates, we consider non-abelian gauge theories featuring either two singlet scalars coupled to gauged fermions via Yuk...

We propose to describe the gauge sector of an asymptotically safe field theory in [Formula: see text] dimensions as a scalar theory on fixed AdS in [Formula: see text]-dimensions using the holographic dictionary.

We introduce a holographic model encapsulating the dynamics of safe quantum field theories.

A bstract We classify all Kutasov-Seiberg type dualities in large N c SQCD with adjoints of rational R -charges. This is done by equating the superconformal index of the electric and magnetic theories: the obtained equation has a solution each time some product of cyclotomic polynomials has only positive coefficients. In this way we easily reproduc...

We present a prescription for using the a central charge to determine the flow of a strongly coupled supersymmetric theory from its weakly coupled dual. The approach is based on the equivalence of the scale-dependent a parameter derived from the four-dilaton amplitude with the a parameter determined from the Lagrange multiplier method with scale-de...

We classify all Kutasov-Seiberg type dualities in large $N_c$ SQCD with adjoints of rational $R$-charges. This is done by equating the superconformal index of the electric and magnetic theories: the obtained equation has a solution each time some product of cyclotomic polynomials has only positive coefficients. In this way we easily reproduce witho...

A bstract Supersymmetric SO(10) models with Yukawa coupling matrices involving only a 10 H and a $$ {\overline{126}}_H $$ 126 ¯ H of Higgs fields can lead to a predictive and consistent scenario for fermion masses and mixings, including the neutrino sector. However, when coupled minimally to a symmetry breaking sector that includes a 210 H and a 12...

Supersymmetric $SO(10)$ models with Yukawa coupling matrices involving only a $10_H$ and a $\overline{126}_H$ of Higgs fields can lead to a predictive and consistent scenario for fermion masses and mixings, including the neutrino sector. However, when coupled minimally to a symmetry breaking sector that includes a $210_H$ and a $126_H$, these model...

We present a prescription for using the a central charge to determine the flow of a strongly coupled supersymmetric theory from its weakly coupled dual. The approach is based on the equivalence of the scale-dependent a-parameter derived from the four-dilaton amplitude with the a-parameter determined from the Lagrange multiplier method with scale-de...

We develop the phenomenology of trinification models based on the gauge group SU(3)C × SU(3)L × SU(3)R which may be realized near the TeV scale. The mass ratios of the fourteen new gauge bosons predicted by these models are determined in terms of a single parameter. Their phenomenology at the LHC is briefly outlined. Generation of singlet neutrino...

We summarize some recent results on residual symmetries in renormalizable SO(10) GUT.

A bstract We investigate the short distance fate of distinct classes of not asymptotically free supersymmetric gauge theories. Examples include super QCD with two adjoint fields and generalised superpotentials, gauge theories without superpotentials and with two types of matter representation and semi-simple gauge theories such as quivers. We show...

We show that in SO(10) models, a Yukawa sector consisting of a real $10_H$, a real $120_H$ and a complex $126_H$ of Higgs fields can provide a realistic fit to all fermion masses and mixings, including the neutrino sector. Although the group theory of SO(10) demands that the $10_H$ and $120_H$ be real, most constructions complexify these fields and...

The Yukawa interactions of the SO(10) GUT with fermions in 16-plets (as well as with singlets) have certain intrinsic ("built-in") symmetries which do not depend on the model parameters. Thus, the symmetric Yukawa interactions of the 10 and 126 dimensional Higgses have intrinsic discrete $Z_2\times Z_2$ symmetries, while the antisymmetric Yukawa in...

We present a new class of unified models based on SO(10) symmetry which provides insights into the masses and mixings of quarks and leptons, including the neutrinos. The key feature of our proposal is the absence of Higgs boson 10_H belonging to the fundamental representation that is normally employed. Flavor mixing is induced via vector-like fermi...

Some aspects of minimal supersymmetric renormalizable grand unified theories are reviewed here. These include some constraints on the model parameters from the Higgs and light fermion masses in SU(5), and the issues of symmetry breaking, doublet–triplet splitting and fermion masses in E 6.

It is a well-known fact that the minimal renormalizable supersymmetric SU(5) model is ruled out assuming superpartner masses of the order of a few TeV. Giving up this constraint and assuming only SU(5) boundary conditions for the soft terms, we find that the model is still alive. The viable region of the parameter space typically features superpart...

We show explicitly that supersymmetric E 6 Grand Unified Theory with a Higgs sector consisting of \( \left\{27 + \overline{27} + {351}^{\prime } + {\overline{351}}^{\prime } + 78\right\} \) fields provides a realistic scenario for symmetry breaking and fermion mass generation. While gauge symmetry breaking can be achieved without the 78 field, its...

We show explicitly that supersymmetric $E_6$ Grand Unified Theory with a Higgs sector consisting of $\{27+\bar{27}+351'+\bar{351'}+78\}$ fields provides a realistic scenario for symmetry breaking and fermion mass generation. While gauge symmetry breaking can be achieved without the $78$ field, its presence is critical for a successful doublet-tripl...

We find an explicit renormalizable supersymmetric $E_6$ model with all the ingredients for being realistic. It consists of the Higgs sector $351'+\overline{351'}+27+\overline{27}$, which breaks $E_6$ directly to the Standard Model gauge group. Three copies of $27$ dimensional representations then describe the matter sector, while an extra $27+\over...

A complete realistic model based on the supersymmetric version of $E_6$ is presented. It consists of three copies of matter 27, and a Higgs sector made of $2\times(27+\bar{27})+351'+\bar{351'}$ representations. An analytic solution to the equations of motion is found which spontaneously breaks the gauge group into the Standard Model. The light ferm...

We review the main constraints on the parameter space of the minimal renormalizable supersymmetric SU(5) grand unified theory. They consist of the Higgs mass, proton decay, electroweak symmetry breaking and fermion masses. Superpartner masses are constrained both from below and from above, giving hope for confirming or definitely ruling out the the...

We study the transition of a scalar field in a fixed $AdS_{d+1}$ background between an extremum and a minimum of a potential. We first prove that two conditions must be met for the solution to exist. First, the potential involved cannot be generic, i.e. a fine-tuning of their parameters is mandatory. Second, at least in some region its second deriv...

We study the transition of a scalar field in a fixed AdS d+1 background between an extremum and a minimum of a potential. We compute analytically the solution to the perturbation equation for the vev deformation case by generalizing the usual matching method to higher orders and find the propagator of the boundary theory operator defined through th...

We show that by adding a vector-like 5+5bar pair of matter fields to the spectrum of the minimal renormalizable SUSY SU(5) theory the wrong relations for fermion masses can be corrected, while being predictive and consistent with proton lifetime limits. Threshold correction from the vector-like fields improves unification of gauge couplings compare...

We present an exactly solvable model of a scalar field in an AdS$_{d+1}$ like background interpolating between a $Z_2$ preserving and a $Z_2$ breaking minima of the potential. We define its holographic dual through the AdS/CFT dictionary and argue that at zero temperature the $d-$dimensional strongly coupled system on the boundary of AdS$_{d+1}$ ex...

We show that simultaneous gauge and supersymmetry breaking can be induced by radiative corrections, a la Coleman-Weinberg. When a certain correlation among the superpotential parameters is present, a local supersymmetry-breaking minimum is found in the effective potential of a gauge non-singlet field, in a region where the tree-level potential is a...

It has been suggested recently that in a consistent theory any Minkowski vacuum must be exactly stable. As a result, a large class of theories that in ordinary treatment would appear sufficiently long-lived, in reality make no sense. In particular, this applies to supersymmetric models in which global supersymmetry is broken in a false vacuum. We s...

Recently, it was suggested that a large class of non-renormalizable theories may need no UV completion. By analogy with gravity where classical black holes are expected to be created in high-energy scatterings, it is conjectured that similar classical solutions, so-called classicalons, should occur. In this way the theory protects itself against no...

The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons at...

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed...

We take the MSSM as a complete theory of low energy phenomena, including neutrino masses and mixings. This immediately implies that the gravitino is the only possible dark matter candidate. We study the implications of the astrophysical experiments such as PAMELA and Fermi-LAT, on this scenario. The theory can account for both the realistic neutrin...

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed...

We study a CP and T violating triple (spin) correlation in the muon to electron conversion in nuclei in the context of the seesaw mechanism. After concluding that the results are negative for all three seesaw types, we turn to the left–right symmetric theories as the original source of seesaw. We find that in general this correlation is of order on...

A good fit of the fermion masses and mixings has been found in the minimal renormalizable supersymmetric SO(10). This solution needs a strongly split supersymmetry breaking scenario with gauginos and higgsinos around 100 TeV, sfermions close to 10^14 GeV and a low GUT scale of around 6 10^15 GeV. We predict fast proton decays through SO(10) type of...

This chapter of the report of the ``Flavor in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure o...

I will describe a minimal supersymmetric SU(5) model, in which the adjoint multiplet breaks spontaneously both gauge and supersymmetry. This inevitably leads to intermediate scales, which in turn increase the GUT scale. The dimension 6 proton decay is thus suppressed, while soft terms coming from supergravity typically dominate.

We study the possibility of obtaining metastable supersymmetry breaking vacua in a perturbative gauge theory without singlet fields, thus allowing for scenarios where a grand unified symmetry and supersymmetry are broken by the same sector. We show some explicit SU(5) examples. The minimal renormalizable example requires the use of two adjoints, bu...

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structu...

We have recently proposed a simple SU(5) theory with an adjoint fermionic multiplet on top of the usual minimal spectrum. This leads to the hybrid scenario of both type I and type III seesaw and it predicts the existence of the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional grand unified theory scale of about 1016 GeV, with ma...

In this talk I will give a short overview of the issue of fermion masses and mixings in SO(10) grandunification. Minimal models as well as absence of any other symmetry will be assumed. We will focus only on low energy or split supersymmetry cases. © 2007 American Institute of Physics

We study the breaking of supersymmetry and its transmission to the light states in the context of the minimal SU(5) grand unified theory, with no additional singlets. This simple theory can be taken as a prototype for a program of breaking simultaneously grand unified symmetry and supersymmetry. The main predictions are: (i) d=6 proton decay is com...

We study the implementation of the type III seesaw in the ordinary nonsupersymmetric SU(5) grand unified theory. This allows for an alternative definition of the minimal SU(5) model, with the inclusion of the adjoint fermionic multiplet. The main prediction of the theory is the light fermionic SU(2) triplet with mass at the electroweak scale. Due t...

I will present a simple, economic and predictive model of Yukawa structures in the context of a renormalizable SO(10) grandunification. The righthanded neutrino mass is generated radiatively. The fermions have Yukawa couplings with one 10 and one 120 dimensional Higgses. In the approxiamate two generation scenario the model predicts degenerate neut...

We discuss the ordinary, nonsupersymmetric SO(10) as a theory of fermion masses and mixings. We construct two minimal versions of the Yukawa sector based on 126̅ H and either 10H or 120H. The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle θA. It also relates the...

The radiative seesaw mechanism of Witten generates the right-handed neutrino masses in SO(10) with the spinorial ${16}_{H}$ Higgs field. We study here analytically the 2nd and 3rd generations for the minimal Yukawa structure containing ${10}_{H}$ and ${120}_{H}$ Higgs representations. In the approximation of small 2nd generation masses and gauge lo...

Neutrino and charged fermion masses provide important constraints on supersymmetric grand unified theories. We illustrate this by focusing on a renormalizable, supersymmetric SO(10) theory proposed long ago, that recently attracted great interest in view of its minimality. We show how the nature of the light Higgs, which depends on the GUT scale fi...

Neutrino and charged fermion masses provide important constraints on grand unified theories. We illustrate this by focusing on a renormalizable, supersymmetric SO(10) theory proposed long ago, that recently attracted great interest in view of its minimality. We show how the nature of the light Higgs, which depends on the GUT scale fields, gets refl...

The seesaw mechanism can explain why the neutrino masses are so tiny with respect to the charged fermion masses. In the canonical version it is the presence of the right-handed neutrino that is responsible for it. In renormalizable grand unified theories with left-right gauge symmetry it is possible to show quite generically that there is another t...

We revive Witten's mechanism for the radiative seesaw induced neutrino masses in SO(10) grand unified theory. We propose its extension to charged fermion masses as a possible cure for wrong tree level mass relations. We offer two simple realizations that can produce a realistic fermionic spectrum. The first one requires two 10-dimensional Higgses i...

We study the nature of the see-saw mechanism in the context of renormalizable SO(10) with Higgs fields in the 10-plets and 126-plet representations, paying special attention to the supersymmetric case. We discuss analytically the situation for the second and third generations of fermions ignoring any CP violating phase. It is shown that b-tau unifi...

We discuss in detail the symmetry breaking and related issues in the minimal renormalizable supersymmetric grand unified theory. We find all the possible patterns of symmetry breaking, compute the associated particle spectrum and study its impact on the physical scales of the theory. In particular, the complete mass matrices of the SU(2) doublets a...

Contents of Part 2: 11. Supersymmetric Grandunification and Fermion Masses (B. Bajc) 12. General Principles of Brane Kinematics and Dynamics (M. Pavsic) 13. Cosmological Neutrinos (G. Mangano) 14. The Problem of Mass (C.D. Froggatt) 15. How to Approach Quantum Gravity ... (D. Grumiller and W. Kummer) 16. Hidden Spacetime Symmetries and Generalized...

A short review of the status of supersymmetric grand unified theories and their relation to the issue of fermion masses and mixings is given.

We show that the minimal renormalizable supersymmetric SO(10) GUT with the usual three generations of spinors has a Higgs sector consisting only of a "light" 10-dimensional and "heavy" 126, 126-bar and 210 supermultiplets. The theory has only two sets of Yukawa couplings with fifteen real parameters and ten real parameters in the Higgs superpotenti...

We briefly review the issues of proton decay and fermion masses and mixings in minimal supersymmetric grand unified theories. We argue that minimal SU(5), although tightly constrained by proton decay data, is still not ruled out. However, we outline the advantages of SO(10) unification, in particular in the model with renormalizable see-saw mechani...

We study the second and third generation masses in the context of the minimal renormalizable SO(10) theory. We show that if the seesaw takes the noncanonical (type II) form, large atmospheric neutrino mixing angle requires b-tau unification.

We review the situation regarding d=5 proton decay in the minimal supersymmetric SU(5) GUT. The minimal theory is defined as the theory with the minimal matter and Higgs content all the way up to the Planck scale; of course, this allows for the possible presence of Planck induced physics. It can be said that either higher dimensional operators must...

We systematically study proton decay in the minimal supersymmetric SU(5) grand unified theory. We find that although the available parameter space of soft masses and mixings is quite constrained, the theory is still in accord with experiment.

Massive neutrinos are a generic prediction of SO(10), and models of unification cry for supersymmetry. Since we have a rather detailed information on neutrino and charged fermion masses, the real question is: how/whether it is possible to build a SO(10) supersymmetric model, that correctly incorporates fermion masses. We show that a simple construc...

It is shown that a realistic SUSY SU(6) GUT can dynamically generate the GUT scale and solve at the same time the doublet-triplet splitting problem. The cosmological implications of such a model are briefly reviewed.

We discuss a supersymmetric SU(6) grand unified theory with the GUT flat direction being lifted by soft supersymmetry breaking, and the doublet–triplet splitting being achieved with Higgs as a pseudo-Goldstone boson. The theory offers a simple solution to the false vacuum and monopole problems.

We study the Higgs sector of a SO(10) grand unified theory which predicts exact conservation of R-parity at all scales and incorporates the see-saw mechanism. We find possible intermediate scales and light states compatible with the constraints coming from the running of the gauge couplings. Such a pattern could lower the SO(10) breaking scale, all...

This is a short review on the subject of symmetry nonrestoration at high temperature. Special emphasis is put on experimental discoveries and different theoretical mechanisms. At the end, possible cosmological applications are briefly mentioned.

We study two issues, the localization of various spin fields, and the problem of the cosmological constant on a brane in five-dimensional anti de Sitter space. We find that spin-zero fields are localized on a positive-tension brane. In addition to the localized zero-mode there is a continuous tower of states with no mass gap. Spin one-half and thre...

It is known that a large neutrino number, of the order of a few percent of the entropy of the universe, leads to symmetry breaking at high temperature. We show here that in the minimal supersymmetric standard model (MSSM) this implies the breaking of electromagnetic charge invariance at T≫MW allowing for the solution of the monopole problem.

We show that intermediate scales in supersymmetric grand unified theories may exist naturally. Their origin is traced to the violation of the survival principle: in supersymmetry internal symmetries often forbid cubic couplings in the superpotential. This leads to a plethora of light supermultiplets whose masses are generated only by higher dimensi...

We analyze the partial rate asymmetry in B+/--->PP¯pi+/- decays (P=pi+, K+, pi0, eta) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for B+/--->chic0pi+/- followed by the decay chic0-->PP¯. The CP violating phase gamma can be extracted from the measured asymmetry. We find that the partial rate asym...

We analyze the pial rate asymmetry in B± → PP̄π ± decays (P = π+, K+, π0, η) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for B± → Xc0π± followed by the decay Xc0 → PP̄. The CP violating phase γ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for B± → π+ π- π...

We analyze the asymmetry in the partial widths for the decays (M=π+,K+,π0,η), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for B±→χc0π± followed by the decay . The CP violating phase γ can be extracted from the measured asymmetry. We find that the partial width asymmetry for B±→π+π−π± is about ,...

We show that the natural presence of flat directions in supersymmetric theories allows for nonrestoration of global and/or gauge symmetries. This has important cosmological consequences for supersymmetric GUTs and in particular it offers a solution of the monopole problem. Comment: 4 pages, 1 Postscript figure, some minor changes and references add...

We analyze the asymmetry in the partial widths for the decays $B^{\pm} \to M {\bar M} \pi^{\pm}$ ($ M = \pi^+, K ^+, \pi^0, \eta$), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for $B^{\pm} \to \chi_{c0} \pi^{\pm} $ followed by the decay $\chi_{c0} \to M {\bar M} $. The CP violating phase $\gamm...

We analyze the semileptonic decay D+-->K-π+l+νl using an effective Lagrangian developed previously to describe the decays D-->Plνl and D-->Vlνl. Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no n...

We analyze the semileptonic decay D+→K-π+l+vl using an effective Lagrangian developed previously to describe the decays D→Plvl and D→Vlvl. Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no new par...

We analyze the partial rate asymmetry in $B^{\pm} \to P {\bar P} \pi^{\pm}$ decays ($ P = \pi^+, K ^+, \pi^0, \eta$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{\pm} \to \chi_{c0} \pi^{\pm} $ followed by the decay $\chi_{c0} \to P {\bar P} $. The CP violating phase $\gamma$ can be extrac...

We analyze the semileptonic decay D+→K−π+l+νl using an effective Lagrangian developed previously to describe the decays D→Plνl and D→Vlνl. Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no new par...

Large charge density, unlike high temperature, may lead to the nonrestoration of global and gauge symmetries. Supersymmetric GUTs with the appealing scenario of unification scale being generated dynamically naturally contain global continuous R symmetries. We point out that the presence of a large R charge in the early Universe can lead to GUT symm...

Large charge density, unlike high temperature, may lead to nonrestoration of global and gauge symmetries. Supersymmetric GUTs with the appealing scenario of unification scale being generated dynamically naturally contain global continuous R-symmetries. We point out that the presence of a large R-charge in the early universe can lead to GUT symmetry...

We analyze the semileptonic decay D{sup +}âK⁻Ï{sup +}l{sup +}ν{sub l} using an effective Lagrangian developed previously to describe the decays DâPlν{sub l} and DâVlν{sub l}. Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant co...

We show that the monopole problem in Grand Unified Theories as well as the domain wall problem may be easily solved if the lepton number asymmetry in the Universe is large enough. Comment: 4 pages, RevTex, some new numerical results and references. To be published in Physical Review Letters

We analyze charm meson semileptonic $D \to V l \nu_l$ and $D\to P l \nu_l$ and nonleptonic $D \to P V$, $D \to PP$ and $D \to VV$ decays within a model which combines the heavy quark effective Lagrangian and chiral perturbation theory.

We analyze $D \to P V$, $D \to PP$ and $D \to VV$ decays within a model developed to describe the semileptonic decays $D \to V l \nu_l$ and $D\to P l \nu_l$. This model combines the heavy quark effective Lagrangian and chiral perturbation theory. We determine amplitudes for decays in which the direct weak annihilation of the initial $D$ meson is ab...

Assuming the ${\bar D}^0, D^-, D^-_s$ and $B^+, B^0, B_s^0$ mesons belong to triplets of SU(3) flavor symmetry, we analyse the form factors in the semileptonic decays of these mesons. Both quark and meson mass differences are taken into account. We find a number of relations, in agreement with the present data as well as with previous analyses, and...

We investigate Cabibbo suppressed $D^{0}$, $D^{+}$ and $D^{+}_{s}$ radiative weak decays in order to find the best mode to test $c\to u \gamma$ decay. Combining heavy quark effective theory and the chiral Lagrangian approach we determine the decay widths. We calculate $\Gamma(D^{0}\to \rho^{0}/\omega\gamma)/ \Gamma(D^{0}\to {\bar K}^{*0} \gamma)$ p...

Theγγ →ρ 0ρ 0 → 4π reaction shows a broad peak at 1.5 GeV in the (J P ,J z )=(2+,2) channel which has no counterpart in theρ +ρ − channel. This “resonance” is considered as a candidate for a qq\(\bar q\);\(\bar q\) state in the “s-channel”. We show, however, that it can also be explained by potential scattering ofρ 0ρ 0 via theσ- exchange in the “t...

The γγ → ρ 0 ρ 0 → 4 π reaction shows a broad peak at 1.5 GeV in the ( J P , J z )=(2+,2) channel which has no counterpart in the ρ + ρ - channel. This “resonance” is considered as a candidate for a qqbar q;bar q state in the “ s-channel”. We show, however, that it can also be explained by potential scattering of ρ 0 ρ 0 via the σ- exchange in the...

It is by now well known that symmetries may be broken at high temperature. However, in renormalizable supersymmetric theories any internal symmetry gets always restored. In nonrenormalizable theories the situation is far less simple. We review here some recent work which seems to indicate that renormalizability is not essential for the restoration...

The $\gamma\gamma\to\rho^0\rho^0\to 4 \pi$ reaction shows a broad peak at 1.5 GeV in the $(J^P,J_z)=(2^+,2)$ channel which has no counterpart in the $\rho^+\rho^-$ channel. This "resonance" is considered as a candidate for a $qq\bar q\bar q$ state in the "s-channel". We show, however, that it can also be explained by potential scattering of $\rho^0...

While it is possible to find examples of field theories with a spontaneously broken symmetry at high temperature, in renormalizable supersymmetric models any internal symmetry gets always restored. Recently, a counterexample was suggested in the context of nonrenormalizable supersymmetric theories. We show that non-negligible higher loop effects ac...

We calculate the one-quark-loop amplitude for the low-energy gammagamma -> pipi collision in the context of the Nambu and Jona-Lasinio model with scalar and pseudoscalar four-quark couplings to all orders in the external momenta. We show that the NJL predictions for the gammagamma -> pi+pi- reaction are not far from the Born amplitude, which is clo...

We analyze charm meson semileptonic decays using the measured ratios $\Gamma_L/\Gamma_T$ and $\Gamma_{+}/\Gamma_{-}$ from $D\to {\bar K}^{*}$ and the branching ratios for $D \to {\bar K}^{*}$ and $D \to {\bar K}$. First we introduce the light vector mesons in a model which combines the heavy quark effective Lagrangian and the chiral perturbation ap...

Combining heavy quark effective theory and the chiral Lagrangian approach we investigate D meson radiative decays. First, we reanalyse $D^{*} \rightarrow D \gamma$ decays using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also the light vector mesons. Then, we calculate branching ratios $D \rightarrow V \gamma$. We make some...