You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
recently , there was a great increase of interest in the study of the physics beyond the standard model , in particularly in the study of the supersymmetric grand unification theories ( susy guts ) .
this interest was in particular stimulated by the new data due to lep1 and lep1.5 experiments .
if one believes literally in all this data , especially in the @xmath1 measurements , one comes to the conclusion that neither the standard model ( sm ) nor the minimal supersymmetric standard model ( mssm ) are sufficient to explain the experimental results @xcite .
one naturally has to turn to the other models .
one of the most popular directions in the search for the new physics is the study of susy guts .
unfortunately , one immediately encounters the problem of how to break supersymmetry ( susy ) .
the most popular way is to use a hidden sector through which susy breaking is transferred to the visible world by means of supergravity ( see e.g. ref.@xcite for a review ) .
recently a new approach to break susy was developed@xcite . in this approach susy
is broken dynamically and the effects of susy breaking are transferred from hidden sector to the visible world by means of gauge interactions .
the natural question is whether one can use this mechanism to construct realistic susy gut theories @xcite .
there are several tools one can use at present to decide whether the gut theory is realistic or not .
one of the most powerful among them is the experimental limit on the proton lifetime .
it was shown in ref.@xcite that simple extension of mimimal su(5 ) susy gut with the mechanism of dynamical susy breaking due to refs .
@xcite leads to the too small lifetime of proton .
consequently , this model is ruled out .
the purpose of this note is to return once again to the analysis of the proton lifetime in the minimal su(5 ) susy gut with dynamical supersymmetry breaking due to dine and nelson , and to include the yukawa couplings in the analysis of ref .
we study the influence of yukawa couplings , both of the 3rd generation and of the hiden sector , on the proton lifetime and masses of the color triplet higgs boson @xmath2 .
we shall see that the inclusion of yukawa couplings increases the proton lifetime but not significantly .
however , the model can not be ruled out at @xmath3 level .
the model is not ruled out in a small window at small @xmath4 if one takes into account the uncertainties in the lep data for @xmath5 and @xmath6 @xmath7 qed and weak coupling constants at @xmath8 scale .
the note is organised in the following way : first we use renormalization group ( rg ) equations for gauge couplings taking yukawa couplings into account .
we then find the masses of color triplet bosons @xmath2 , depending on @xmath9 ( qcd coupling ) for different values of @xmath10 , @xmath11 .
we then use the formula for proton lifetime from ref.@xcite to find the proton lifetime for different allowed by lep data values of @xmath5 and @xmath6 , @xmath9 .
our final results are depicted in figs.1 - 6 , thus giving the bounds on the possibility of using mechanism of refs.@xcite to break susy in su(5 ) gut model .
let us briefly describe the model we are going to study ( we refer to the reader to refs.@xcite for details ) .
the model is the mimimal su(5 ) susy gut plus the messenger superpotential @xmath12 here l and d , that carry quantum numbers of sm gauge groups and form together into @xmath13 of su(5 ) , are the messenger lepton and quark chiral superfields added to the model .
s is a scalar chiral superfield singlet under the sm gauge groups .
s transfers the supersymmetry breaking from hidden sector to the fields of the standard model . at the messenger scale @xmath14 tev
the singlet s and its f - component get vacuum expectation values and susy breaks down .
the heavy superfields l and d transfer the information of susy breaking to the fields of sm through their couplings to the sm gauge groups .
the analysis of proton decays in this note is similiar to the work by carone and murayama@xcite .
however , these authors did not take into account the influence of the yukawa couplings on the evolution of gauge couplings .
we use below the rg equations for yukawa couplings that can be derived using ref.@xcite .
first , we evolute the rg equaions from @xmath8 to @xmath15 using the sm @xmath16-functions and then from @xmath15 to @xmath17 ( taken as 100tev ) using the mssm ones . above @xmath17 we take into account the effects of the messenger fields : @xmath18 the evolution of yukawa couplings themselves are taken into account in one loop approximation and are carried out using the following rg equations ( for scales larger than @xmath17 ) : @xmath19 our notations are self - evident : @xmath20 and @xmath21 are yukawa couplings of @xmath22 , @xmath23 , and @xmath0 to the corresponding higgs doublets in the miminal su(5 ) susy model . @xmath24 and @xmath25 are the messenger yukawa coupling constants to the singlet s. we proceed then in the same way as in ref .
we use the evolution of @xmath10 and @xmath11 to determine the gut scale @xmath26 where @xmath10 and @xmath11 unify into @xmath27 , and then get the mismatch between @xmath28 and @xmath29 , which should be attributed to the gut threshold effects , that are assumed to originate from the color triplet @xmath30 .
we get the mass of the color - triplet higgs @xmath31 from its dependence on the threshold effects ( the detailed formulae can be found in @xcite ) .
once @xmath31 is determined , we use the standard formulae for the proton lifetime(see ref .
@xcite ) to find the partial width and to compare them with the current experimental bounds .    in our numerical evolution , we use the following boundary conditions .
first , we made a standard choice of the masses of @xmath32-quark , @xmath0-lepton and the top - quark as : @xmath33 gev , @xmath34 gev and @xmath35 gev .
we do not depict uncertainties in these boundary conditions due to masses , since their influence on the results is not large .
for the messenger yukawa couplings we take the largest possible values : @xmath36 if we choose the boundary conditions to be given by eq .
( [ 7 ] ) , @xmath24 and @xmath25 unify into a common value at the gut scale .
if inputs larger than those in ( [ 7 ] ) is taken , the messenger yukawa couplings will blow up at the gut scale .
the boundary conditions for gauge couplings are determined from lep data@xcite : @xmath37 for the qcd coupling we use @xmath38 @xcite  the number that incorporates both low energy data and lep1 data .
all the gauge couplings are taken within @xmath3 variations in our estimations .
our main results are depicted in figs . 1 - 6 .
first , we depict the mass of the color - triplet , @xmath31 , as a function of @xmath9 for different @xmath4 .
these results are depicted in fig . 1 - 3 for different values of @xmath5 and @xmath6 .
we take the lowest bound of @xmath4 as 0.85 . below this
bound the yukawa couplings will blow up at the gut scale .
this lowest bound can be achieved only when the yukawa couplings are included in the rg analyses .
we see that for reasonable values of @xmath4 , yukawa couplings of messenger quarks and leptons actually do not influence @xmath31 greatly .
however , when we consider the different values of @xmath10 and @xmath11 within @xmath3 variations , we see that @xmath31 can change quite significantly as a function of @xmath5 and @xmath6 .
the most favored @xmath31 is gained when @xmath5 is taken at its upper bound while @xmath6 the lower one .
next , we consider the decay rate of a typical process @xmath39 . this mode was argued in ref .
@xcite to be the most appropriate one in analysing proton decay bound in susy gut .
the results are shown in figs .
we see that the allowed region of @xmath40 and @xmath4 depends on the inputs @xmath5 and @xmath6 .
inclusion of the usual yukawa couplings in rg equations improves the situation with the proton lifetime . on the other hand , inclusion of the messenger yukawa couplings
even worses the situation slightly . as the current experimental bound@xcite of proton decay lifetime
is concerned , the only window where the model survives is the region of small @xmath4 combined with large @xmath5 and small @xmath6 as input .
our general conclusions are that , first , the inclusion of yukawa couplings does not lead to significant changes in the mass of color triplet and the allowed parameter space for the model we consider .
second , the allowed parameter space , color triplet mass and proton lifetime seem to be quite sensitive to exact values of @xmath10 and @xmath11 at @xmath41 scale .
the authors thank m. shifman for useful discussion .
99 j. hewett , talk at workshop on heavy flavors , technion , december 1995 .
j. ellis , invited talk at lp95 : international symposium on lepton photon interactions ( ihep ) , beijing , p.r .
china , 10 - 15 aug 1995 .
cern - th-95 - 316 , hep - ph/9512335 m. shifman , talk at workshop on heavy flavors , technion , december 1995 .
nilles , phys . rep .
110 , 1 ( 1984 ) .
m. dine and ann e. nelson , phys.rev.d48 , 1277 ( 1993 ) .
m. dine , ann e. nelson and shirman , phys.rev.d51 , 1362 ( 1995 ) .
m. dine , a. e. nelson , y. nir and y. shirman , scipp-95 - 32 , hep - ph/9507378 . c. d. carone and h. murayama , lbl-37810 , ucb - pth-95/32 , hep - ph/9510219 .
m. e. machacek and m. t. vaughn , nucl .
b222 , 83 ( 1983 ) ; nucl .
b236 , 221(1984);nucl .
b249 , 70 ( 1985 ) .
s. p. martin and m. t. vaughn , phys .
d50 , 2282 ( 1994 ) .
j. erler and p. langacker , phys .
d52 , 441 ( 1995 ) .
j. hisano , h. murayama , and t. yanagida , nucl .
b402 , 46 ( 1993 ) .
particle data group , phys .
d50 , 3-i ( 1994 ) .
fig . 1 the dependence of the color triplet boson mass on @xmath4 and @xmath9 , when @xmath5 and @xmath6 are both taken as central values of experiment results .
the dotted and the dash - dotted lines correspond to the results without any yukawa couplings and with only messenger yukawa couplings , respectively .
the dashed and solid lines correspond to results with all yukawa couplings included for @xmath42 and @xmath43 , respectively .
4 @xmath9 and @xmath4 plane excluded by the proton decay constraint , when @xmath5 and @xmath6 are both taken their central values .
the dash - dotted , dashed and solid lines correspond to the cases without yukawa couplings , with only messenger yukawa couplings , and with all yukawa couplings included , respectively .
we study the influence of messenger yukawa couplings and top , bottom and @xmath0 yukawa couplings on the proton lifetime in su(5 ) supersymmetric gut with dynamical supersymmetry breaking mechanism due to dine and nelson .    
 = -1 cm = -1 cm = 0.2 cm    hep - ph/9602310    technion - ph-96 - 5    february , 1996    proton lifetime , yukawa couplings and dynamical susy breaking in su(5 ) gut    boris blok , cai - dian l and da - xin zhang    physics department , technion- israel institute of technology ,    haifa 32000 , israel