A WEAK-(p, q) INEQUALITY FOR FRACTIONAL INTEGRAL OPERATOR ON MORREY SPACES OVER METRIC MEASURE SPACES

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1 JMP : Volume 8 Nomor, Juni 206, hal -7 A WEAK-p, q) INEQUALITY FOR FRACTIONAL INTEGRAL OPERATOR ON MORREY SPACES OVER METRIC MEASURE SPACES Idha Sihwaningrum Department of Mathematics, Faculty of Mathematics and Natural Siences Jenderal Soedirman University idha.sihwaningrum@unsoed.ac.id Abstract. This paper presents a weak-p, q) inequality for fractional integral operator on Morrey spaces over metric measure spaces of nonhomogeneous type. Both parameters p and q are greater than or equal to one. The weak-p, q) inequality is proved by employing an inequality involving maximal operator on the spaces under consideration. Keywords: Fractional integral operator, maximal operator,morrey spaces, nonhomogeneous, weak type inequality.. Introduction Fractional integral operator, which is firstly defined by Hardy and Littlewood, 927), is an inverse for a power of the Laplacian operator on Euclidean spaces. This operator is also called the Riesz potential. Riesz 938) introduced the potential as an extension of the Newtonian potential. Nowadays, it can be found that the works on fractional integral operator have been developed in some directions. For examples, Adams, 975), Nakai, 994), Kurata, et al., 2002), Gunawan and Shwaningrum, 203) and Eridani, et al., 204) provided some results on homogeneous type spaces; meanwhile García-Cuerva and Martell, 200), Liu and Shu, 20), Sihwaningrum, et al., 202), and Sawano an Shimamura, 203) provided some results on nonhomogeneous type spaces. A metric measure space, d, µ) is a homogeneous type space if the Borel measure µ satisfies the doubling condition, that is there exists a positive constant C such that for every ball Ba, r) the condition µbx, 2r)) CµBx, r)) ) holds. In equation ), a is the center of the ball and r is the radius of the ball. If the doubling condition does not hold, then we have a metric measure space of nonhomogeneous type. In spaces of nonhomogeneous type, the doubling condition can be replaced by the growth condition µbx, r)) C r n 2) where n is less than or equal to the dimension of the metric measure spaces. The action on the spaces of nonhomogeneous type goes back to the works of Nazarov, et al., 998), Tolsa, 998), and Verdera, 2002).

2 2 I. SIHWANINGRUM In the metric measure spaces of nonhomogeneous type, García-Cuerva and Gatto, 2004) defined the fractional integral operator I α to be I α fx) := fy). 3) The fractional integral operator equation 3)) has been proved to satisfy the weak-, q) an inequality in Lebesgue spaces over metric measure spaces of nonhomogeneous type García-Cuerva and Gatto, 2004), in Morrey spaces over metric measure of non homogenenous type Sihwaningrum, 206) and in generalized Morrey spaces over metric measure spaces of non homogeneous type Sihwaningrum, et al., 205). This kind of weak type is also established in Sihwaningrum and Sawano, 203) for another version of fractional integral operator. The weak inequalities measure the size of the distribution function Duoandikoetxea, 200). As Hakim and Gunawan, 203) had a result on the weak-p, q) inequality where p q < ) for fractional integral operator in the generalized Morrey spaces over Euclidean spaces of nonhomogeneous type, the results on the weak-, q) inequality on Morrey spaces over metric measure spaces of nonhomogeneous type will extended in this paper into a weak-p, q) inequality. Morrey spaces were first introduced by Morrey, 940); and in this paper, Morrey spaces over metric spaces of non homogeneous type L p,λ µ) := L p,λ, µ) for p < and 0 λ < n) contain all functions in L p loc in which f p L p,λ µ) := sup Bx,r) µbx, 2r))) λ Bx,r) ) /p <. 2. Main Results To prove the weak-p, q) inequality of fractional integral operator on Morrey spaces over metric measure spaces of nonhomogeneous type, we need the following inequality which involves maximal operator M. This operator is defined by Mfx) := sup x suppµ)) 4) r>0 µbx, 2r)) Bx,r) Sawano, 2005). Some properties of maximal operator M can be found for example in Terasawa, 2006). Note that from now on, C denotes different positive constants. Theorem 2.. Let χ Ba,r) be the characteristic function of ball Ba, r). If f L p,λ µ) for p < and 0 < λ <, then for any ball Ba, r) on we have Mχ Ba,r) Cr nλ f p L p,λ µ).

3 A WEAK-p, q) INEQUALITY FOR FRACTIONAL INTEGRAL OPERATOR 3 Proof. By applying the growth condition in equation 2), for any function f in L p,λ µ) we get Mχ Ba,r) Ba,r) C Mχ Ba,r) + Ba,r) + j= 2 jn j= Ba,2 j+ r)\ba,2 j r) Ba,2 j+ r)\ba,2 j r) C f p µba, 2r)) λ + 2 jn µba, 2 j+2 r)) λ L p,λ µ) j= C f p 2r) nλ + 2 jn 2 j+2 r) nλ L p,λ µ) j= = Cr nλ f p + L p,λ µ) j= 2 jn λ). Mχ Ba,r) Since λ > 0, then j= 2 jn λ) is convergent. As a result, Mχ Ba,r) Cr nλ f p L p,λ µ). Therefore, the proof is complete. Having Theorem 2., we are now able to get the weak-p, q) inequality for fractional integral operator I α. Theorem 2.2. Let 0 < α < n, p q <, and 0 λ < αp q = p α n λ), then n. If ) q f L µ {x Ba, r) : I α fx) > }) Cr nλ p,λ µ). Proof. For any positive R, we can write I α fx) as I α fx) Bx,R) = A + A 2. + \Bx,R)

4 4 I. SIHWANINGRUM An estimate for A 2 is A 2 = dx,y) R Bx,2 j+ R)\Bx,2 j R) 2 j R) 2 2n 2 j R) α 2 j+2 R) n Bx,2 j+ R) Bx,2 j+ R). Since µ satisfies the growth measure condition, then R α 2 jα A 2 µbx, 2 j+2 R)) Bx,2 j+ R) ) /p CR α 2 jα µbx, 2 j+2 R)) Bx,2 j+ R) = CR α 2 jα µbx, 2 j+ R)) /p µbx, 2 j+2 R)) λ/p µbx, 2 j+2 R)) λ CR α f L p,λµ) 2 j+ R ) n /p) 2 j+2 R ) nλ/p CR α+nλ/p /p) f L p,λ µ) 2 jα+nλ/p /p)). By using the assumption 0 λ < αp n, we find that convergent; and hence A 2 CR α+ n p λ ) f L p,λ µ). Bx,2 j+ R) Bx,2 j+ R) 2jα+nλ/p /p)) is Now, an estimate for A is given by ) /p ) /p A Bx,R) Bx,R) ) /p µbx, ) /p R)) Bx,R) R ) /p ) CR n /p Bx,R) R ) /p CR α /p). Bx,R) ) /p ) /p If we let CR α+ n p λ ) f L p,λ µ) = 2,

5 A WEAK-p, q) INEQUALITY FOR FRACTIONAL INTEGRAL OPERATOR 5 then A 2 2 and { x Ba, r) : A 2 > 2 } =. As a result, µ {x Ba, r) : I α fx) > }) { µ x Ba, r) : A > }) { 2 = µ x Ba, r) : A > }) 2 = µ x Ba, r) : CRα /p) { = µ x Ba, r) : C R α /p)) p p = C R α /p)) p p CRαp ) p CRαp ) p Bx,R) Ba,r) Bx,R) { + µ x Ba, r) : A 2 > }) 2 Bx,R) > Bx,R) By,R) ) /p > 2 }) ) p 2CR α /p) dµx) χ Ba,r) x) χ Ba,r) x) dµx) R α Mχ Ba,r) y). Furthermore, Theorem 2. enables us to find dµx) ) µ {x Ba, r) : I α fx) > }) CRαp ) R α r nλ p f p L p,λ µ) As q = p α n λ) give us = Cr nλ R α f L p,λ µ) ) p. R α ) p ) q f L p,λ µ) f L = CR n λ) p,λ µ) =, then we end up with µ {x Ba, r) : I α fx) > }) Cr nλ f L p,λ µ) This is our desired inequality. ) q. 3. Concluding Remarks The results in this paper can be reduced to the result in Sihwaningrum, 206) if p =. Besides, the proof of the weak-p, q) inequality for fractional integral operator on Morrey spaces over metric measure spaces of nonhomogeneous type can be found by using other methods. One of the common methods is a proof by using Hedberg type inequality. Acknowledgments. This paper is a result of Fundamental Research Program 205, Directorate General of Higher Education, Indonesia, No. 20/UN23.4/PN/205.

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