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:
particle physics candidates for dark matter abound , the most popular being the lightest neutralino of supersymmetric models such as the minimal supersymmetic standard model ( mssm ) and its extensions . on the other hand ,
non - supersymmetric models also have their own dark matter candidate , the most popular one being the axion . introduced by peccei and quinn @xcite long ago to solve the strong cp problem , the axion has required an extra global @xmath1 symmetry , attached to the fields of the standard model ( sm ) .
its inclusion in a supersymmetric lagrangean has also always required the introduction of an extra global symmetry , together with a supersymmetric partner ( the axino ) . to bring both components ( the axion and the neutralino ) under the spell of the gauge principle requires , quite likely , a gauging of the axionic symmetries .
the study of axionic symmetries and of their gauging is an important aspect of string theory at lower energy , being connected with the presence , in these effective models , of several moduli fields , deprived of a potential and derived from geometrical compactifications .
the attempt to match these descriptions with effective models ( with or without supersymmetry and gravity ) based on ordinary quantum field theory and supersymmetry ( in flat space ) is pursued in several works @xcite @xcite , where the role of the anomalous interactions and of light pseudoscalars is investigated under the tenets of gauge invariance and unitarity @xcite .
in general , these effective field theories are characterized by the presence of higher dimensional operators to correct for the exposed ( axial ) anomaly ( in the form of wess - zumino terms with stckelberg axions ) @xcite .
their gauge structure , in fact , requires at least one extra anomalous @xmath1 interaction .
the presence of gauge couplings and of a mass for this axion not related by the same suppression scale ( @xmath2 ) - which is of the order of @xmath3 gev for a traditional ( ungauged ) axion - makes this new axion a very attractive dark matter candidate .
however , building axion models with gauged axionic symmetries is rather challenging from the field theory point of view since it requires a grasp of the unusual features of the chiral anomaly , from the organization of the effective action(s ) to the presence of anomaly poles that challenge the consistency of the s - matrix in some of their scattering amplitudes @xcite .
one of the realizations of field theories which contain axion - like particles in their spectrum is the minimal low - scale orientifold model ( mlsom ) @xcite , based on a construction involving charge assignments obtained from intersecting branes .
these models introduce one stckelberg axion for each anomalous @xmath1 present in the gauge structure . in @xcite
it is shown that the physical spectrum of the mlsom contains always one physical axion , independently of the number of anomalous u(1 ) s .
supersymmetric extensions of these class of models have been discussed rather recently @xcite , using a superpotential which is the one typical of the ussm @xcite , extending previous studies respect to the mssm , the ussm contains an extra singlet superfield and an extra u(1 ) gauge symmetry , which is anomaly free . in the ussm - a model of @xcite , which is the theory proposed as a possible supersymmetric extension of the mlsom ,
this symmetry has been left anomalous , and the bosonic mechanism of cancellation of these anomalies , which is enforced via the inclusion of wess - zumino ( counter)terms , has been generalized .
these models contain a combined higgs - stckelberg mechanism for the generation of the mass of the anomalous gauge bosons .
a physical axion state ( the axi - higgs ) appears quite naturally , together with its supersymmetric partner , the axino .
this second state becomes a component of the fermionic neutralinos , after diagonalization of the mass matrix of the neutral fermion sector .
compared to other constructions , in which the axion disappeares from the physical spectrum being just a goldstone mode , in the ussm - a the presence of the extra singlet superfield allows a physical projection of the stckelberg axion of the model on the axi - higgs ( @xmath4 ) .
therefore this physical state inherits direct axion - like couplings ( such as @xmath5 ) to the gauge fields , becoming a gauged supersymmetric axion @xcite .
the particle is massless in the absence of peccei - quinn - breaking potentials , in which the axion appears as a phase , while the instanton vacuum can naturally lift its mass up to @xmath6 ev as in the peccei quinn ( invisible axion ) case .    in the non - supersymmetric version of these theories , i.e. in the mlsom , one of the special features of these theories is the presence of anomalous trilinear gauge interactions , which are totally absent in the standard model ( sm ) due to anomaly cancellation @xcite .
we just recall that in the sm these interactions are suppressed and appear only away from the chiral limit in @xmath7 diagrams ( for instance in @xmath8 vertices ) .
we show in fig . 1 results for the production of two axions @xmath9 in the mlsom at the tevatron ( left panel ) and at the lhc ( right panel ) , as a function of the invariant mass @xmath10 of the final state , obtained from a recent analysis .
the gluon fusion chnnel is the most important one for their study .
the processes involve the usual triangle diagrams as for the production of the higgs sector . in our case
we have considered two higgs doublets @xmath11 in the cp - even sector .
the s - channel exchange involves either an @xmath12 , a @xmath13 or a @xmath4 .
we have selected a mass of the @xmath14 gev and of @xmath15 gev for the @xmath13 , with @xmath16 gev .
the search for light ( gauged ) pseudoscalars is for sure a challenge for the experimental acvitity at the lhc @xcite , requiring precise evaluation of the qcd background .
however , while the detection of anomalous extra z prime which modify the neutral current sector of these theories remains difficult , the identification of a light pseudoscalar ( in the mass range of 1 to 10 gev ) , which is their second signature , is more favoured .
we thank roberta armillis and luigi delle rose for discussions .
this work was supported ( in part ) by the european union through the marie curie research and training network `` universenet '' ( mrtn - ct-2006 - 035863 ) .
peccei and h.r .
quinn , phys .
d16 ( 1977 ) 1791 . c. corian , n. irges and s. morelli , jhep 07 ( 2007 ) 008 , hep - ph/0701010 . c. corian , n. irges and s. morelli , nucl .
b789 ( 2008 ) 133 , hep - ph/0703127 .
p. anastasopoulos , f. fucito , a. lionetto , g. pradisi , a. racioppi , y. s. stanev phys.rev.d78:085014 , 2008 .
r. armillis et  al .
, jhep 10 ( 2008 ) 034 , 0808.1882 . c. corian , m. guzzi and s. morelli , eur .
j. c55 ( 2008 ) 629 , 0801.2949 . c. corian , n. irges and e. kiritsis , nucl .
b746 ( 2006 ) 77 , hep - ph/0510332 . c. corian , m. guzzi , a. mariano , s. morelli , ( 2008 ) , 0811.3675 .
m. cvetic , d.a .
demir , j.r .
espinosa , l.l everett , p. langacker , phys . rev .
d56 ( 1997 ) 2861 , hep - ph/9703317 . c. corian , m. guzzi , n. irges , nikos , a. mariano , ( 2008 ) , 0811.0117 .
r. armillis , c. corian and m. guzzi , jhep 05 ( 2008 ) 015 , 0711.3424 .
r. armillis , c. corian , m. guzzi , s. morelli , ( 2008 ) , 0809.3772 .
axion - like particles are an important part of the spectrum of anomalous gauge theories involving modified mechanisms of cancellation of the gauge anomalies . among these 
 are intersecting brane models , which are characterized by the presence of one physical axion . 
 we overview a recent study of their supersymmetric construction and some lhc studies of the productions rates for a gauged axion .    _ 
 @xmath0dipartimento di fisica , universit del salento + and infn sezione di lecce , via arnesano 73100 lecce , italy _ +