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the low - energy interaction between hadrons contains a parity - violating ( pv ) component due to the weak interactions of quarks contained in the hadrons . hadronic parity violation has received renewed interest with a number of ongoing and planned experiments @xcite as well as theoretical developments . traditionally , there are two different theoretical approaches to hadronic parity violation . the most commonly used framework is the one - meson exchange model of desplanques , donoghue and holstein ( ddh ) @xcite . in a different approach by danilov @xcite the pv hadronic interactions are described in terms of 5 low - energy amplitudes . more recently , effective field theories ( efts ) have been applied to the problem of hadronic parity violation @xcite . here we present results of calculations in the framework of pionless effective field theory ( ) . in only nucleon fields appear as dynamic degrees of freedom . at the energies of many of the current and planned experiments the pion can not be resolved and can be integrated out . the remaining interactions are given in terms of 5 @xmath1 contact terms , each accompanied by an unknown low - energy constand ( lec ) . while the lecs can not be predicted within the theory , once they have been determined by comparison with a sufficient number of experimental data the theory has predictive power . as an eft this approach is model - independent and allows for a systematic improvement of the results . the results presented here constitute an important step in the determination of the pv low - energy constants . in all interactions are described by contact terms . in the parity - conserving sector the lagrangian is given by @xmath2 where @xmath3 and @xmath4 are su(2 ) pauli matrices in spin and isospin space , respectively , @xmath5 is the nucleon covariant derivative , @xmath6 and @xmath7 and @xmath8 are the isoscalar and isovector nucleon magnetic moments . the partial wave projection operators are defined through @xcite @xmath9 in the power - divergence subtraction scheme @xcite , which we employ in our calculations , the low - energy couplings are given by @xmath10 with @xmath11 ( @xmath12 ) the @xmath13 ( @xmath14 ) scattering length and @xmath15 the renormalization point . for the leading - order pv lagrangian we use the formulation given in @xcite , @xmath16 + h.c.,\end{aligned}\ ] ] where @xmath17 with @xmath18 some spin - isospin - operator , and @xmath19 nucleon - nucleon scattering is theoretically the most basic process in which to study hadronic parity violation . the longitudinal asymmetry @xmath20 where @xmath21 is the total scattering cross section of a polarized nucleon with helicity @xmath22 on an unpolarized nucleon target , would vanish if parity were conserved . with the lagrangians given in sec . [ sec : lags ] and neglecting coulomb interactions for the @xmath23 case we obtain at leading order @xmath24 and @xmath25 with @xmath26 linear combinations of the parameters of the lagrangian , and @xmath27 the differential cross section in partial wave @xmath28 . since @xmath29 is an observable and therefore independent of the renormalization point @xmath15 , the @xmath15-dependence of @xmath30 is dictated entirely by @xmath31 . in addition , since the energy dependence of the differential cross sections in the @xmath32 and @xmath33 partial waves differ , a detailed study of the energy dependence of the @xmath34 asymmetry in principle allows an extraction of two different linear combinations of the pv parameters . the result of eq . ( [ nn : ppnn ] ) does not take into account coulomb effects for the @xmath23 case . coulomb interactions can be systematically incorporated in . we find that at energies for which is applicable coulomb corrections turn out to be small and can be treated perturbatively @xcite . there exist two experimental results for @xmath35 at @xmath36 @xcite and @xmath37 @xcite . while the result at @xmath36 can be used to extract the combination @xcite @xmath38 the energy of @xmath37 lies outside the domain of applicability of . by choosing suitable neutron polarizations the reaction @xmath0 allows access to two different pv observables . for polarized neutrons one can determine the photon asymmetry @xmath39 at threshold , which is defined through @xmath40 where @xmath41 is the @xmath0 width and @xmath42 the angle between the neutron polarization and the direction of the outgoing photon momentum . at leading order we obtain @xmath43 note again the appearance of a ratio of pv and pc couplings , indicating that any renormalization point dependence in the weak couplings is driven by those in the strong coupling . we would also like to point out that we do not require phenomenological wave functions for the deuteron , but treat the deuteron field consistently in the eft framework . there is an ongoing experimental effort at the spallation neutron source to measure @xmath39 to a sensitivity of @xmath44 ( see e.g.  @xcite ) .    for unpolarized neutron capture the pv interactions induce a circular polarization of the outgoing photon @xmath45 , @xmath46 where @xmath47 is the total cross section for photons with positive / negative helicity . the leading - order result is given by @xmath48.\end{aligned}\ ] ] the asymmetry in the inverse reaction might be experimentally more feasible and is equal to @xmath45 for exactly reversed kinematics . current experimental results are consistent with zero in both cases @xcite . we have presented results for two - body pv observables in the framework of pionless effective field theory , in particular asymmetries in @xmath1 scattering and polarized radiative neutron capture , and an induced photon polarization in unpolarized neutron capture . these results provide an important step in the determination of the unknown low - energy constants in the pv lagrangian of eq . ( [ lag : pv ] ) . in order to determine all five parameters it is necessary to also consider few - body processes . in the future we will look at observables such as , e.g. , asymmetries in @xmath49 or @xmath50 spin rotation for which experiments are ongoing or being considered . i thank d.r . phillips and r.  p.  springer for their collaboration on the topics presented here and many interesting discussions , as well as useful comments on the manuscript . this work was supported by the us department of energy under grant de - fg02 - 93er40756 and grant de - fg02 - 05er41368 . i also acknowledge financial support by the national science foundation ( career grant phy-0645498 ) and us department of energy ( de - fg02 - 95er-40907 ) . e.  stiliaris , eur . phys .  j.   a * 24s2 * , 175 ( 2005 ) . b.  lauss _ et al . _ , aip conf . * 842 * , 790 ( 2006 ) [ arxiv : nucl - ex/0601004 ] . c.  d.  bass _ et al . _ , arxiv:0905.0395 [ nucl - ex ] . b.  desplanques , j.  f.  donoghue and b.  r.  holstein , annals phys .   * 124 * , 449 ( 1980 ) . g.  s.  danilov , phys . lett . * 18 * , 40 ( 1965 ) ; phys . * b35 * , 579 ( 1971 ) . * 14 * , 443 ( 1972 ) . d.  b.  kaplan , m.  j.  savage , r.  p.  springer and m.  b.  wise , phys . b * 449 * , 1 ( 1999 ) [ arxiv : nucl - th/9807081 ] . m.  j.  savage and r.  p.  springer , nucl . a * 644 * , 235 ( 1998 ) [ erratum - ibid . a * 657 * , 457 ( 1999 ) ] [ arxiv : nucl - th/9807014 ] . m.  j.  savage , nucl . a * 695 * , 365 ( 2001 ) [ arxiv : nucl - th/0012043 ] . s.  l.  zhu , c.  m.  maekawa , b.  r.  holstein , m.  j.  ramsey - musolf and u.  van kolck , nucl . a * 748 * , 435 ( 2005 ) [ arxiv : nucl - th/0407087 ] . d.  b.  kaplan , m.  j.  savage and m.  b.  wise , phys . c * 59 * , 617 ( 1999 ) [ arxiv : nucl - th/9804032 ] . d.  b.  kaplan , m.  j.  savage and m.  b.  wise , phys . b * 424 * , 390 ( 1998 ) [ arxiv : nucl - th/9801034 ] . d.  b.  kaplan , m.  j.  savage and m.  b.  wise , nucl . b * 534 * , 329 ( 1998 ) [ arxiv : nucl - th/9802075 ] . d.  eversheim _ et al . _ , phys . b * 256 * ( 1991 ) 11 ; p. d.  eversheim _ et al . _ , spring meeting of the dpg , salzburg 1992 , abstract in verhandlungen der dpg ( 1992 ) 59 ; w.  haeberli and b.  r.  holstein , arxiv : nucl - th/9510062 . s.  kistryn _ et al . _ , phys . lett .   * 58 * , 1616 ( 1987 ) . c.  b.  crawford , 4th international workshop `` from parity violation to hadronic structure and more  '' , 22 - 26 june 2009 , bar harbor , ` http://web.mit.edu/pavi09/talks/crawford_neutron_cap_pv.pdf ` .
we present results for two - body observables that are sensitive to the parity - violating component of nucleon - nucleon interactions . 
 these interactions are studied using an effective field theory in which the only dynamic degrees of freedom are nucleon fields . 
 the observables we study are cross - section asymmetries in nucleon - nucleon scattering and asymmetries and induced polarizations in the process @xmath0 .