Let $ \mathcal{K}^n $ denote the set of convex bodies (compact, convex subsets with non-empty interiors) in Euclidean space $ \mathbb{R}^n $. The set of convex bodies containing the origin in their interiors, we write $ \mathcal{K}_o^n $. $ \mathcal{S}_o^n $ denotes the set of star bodies (about the origin) in $ \mathbb{R}^n $. The unit ball in $ \mathbb{R}^n $ and its surface will be denoted by $ B $ and $ S^{n-1} $, respectively. $ V(K) $ denotes the $ n $-dimensional volume of a body $ K $ and write $ V(B) = \omega_n $.
For $ K\in \mathcal{K}^n $, its support function, $ h_K $ = $ h(K, \cdot) $: $ \mathbb{R}^n\rightarrow\mathbb{R} $, is defined by (see [1, 2])
where $ x\cdot y $ denotes the standard inner product of $ x $ and $ y $.
The conception of $ L_p $-centroid body was introduced by Lutwak and Zhang (see [3]). For each compact star-shaped (about the origin) $ K $ in $ \mathbb{R}^n $ and real $ p\geq1 $, the $ L_p $-centroid body, $ \Gamma_p K $, of $ K $ is an origin-symmetric convex body which support function is defined by
for any $ u\in S^{n-1} $, where the integration is in connection with Lebesgue measure on $ S^{n-1} $ and
In 2000, Lutwak, Yang and Zhang in [4] put forward the notion of $ L_p $-projection body. For $ K\in\mathcal{K}_o^n $ and real $ p\geq1 $, the $ L_p $-projection body, $ \Pi_p K $, of $ K $ is an origin-symmetric convex body whose support function is given by
for all $ u\in S^{n-1} $. Here $ S_p(K, \cdot) $ is the $ L_p $-surface area measure of $ K $,
and $ c_{n-2, p} $ satisfies (1.2). At the same time, they (see [4]) proved the $ L_p $-Petty projection inequality and $ L_p $-Busemann-Petty centroid inequality. For the $ L_p $-centroid bodies and $ L_p $-projection bodies, some scholars made a series of researches and gained several results (see [5-15]). In particular, Wang, Lu and Leng in [12] established the following monotonic inequalities.
Theorem 1.A Let $ K, L\in \mathcal{K}^n_o $ and $ p\geq1 $. If for any $ Q\in\mathcal{K}^n_o $, $ V_p(K, Q)\leq V_p(L, Q) $, then $ V(\Pi_p K) \leq V(\Pi_p L) $ with equality for $ p = 1 $ if and only if $ \Pi_p K $ and $ \Pi_p L $ are translates, for $ p>1 $ if and only if $ \Pi_p K = \Pi_p L $, here $ V_p(M, N) $ denotes the $ L_p $-mixed volume of $ M, N\in\mathcal{K}^n_o $.
Theorem 1.B Let $ K, L\in \mathcal{K}^n_o $ and $ p\geq1 $. If for any $ Q\in\mathcal{K}^n_o $, $ V_p(K, Q)\leq V_p(L, Q) $, then $ V(\Pi_p^\ast K) \geq V(\Pi_p^\ast L) $ with equality if and only if $ \Pi_p K = \Pi_p L $, here $ \Pi_p^\ast M $ denotes the polar of $ \Pi_p M $.
Theorem 1.C Let $ K, L\in \mathcal{S}^n_o $ and $ p\geq1 $. If for any $ Q\in\mathcal{S}^n_o $, $ \widetilde{V}_{-p}(K, Q)\leq \widetilde{V}_{-p}(L, Q), $ then
with equality for $ p = 1 $ if and only if $ \Gamma_p K $ and $ \Gamma_p L $ are translates, for $ p>1 $ if and only if $ \Gamma_p K = \Gamma_p L $, here $ \widetilde{V}_{-p}(M, N) $ denotes the $ L_p $-dual mixed volume of $ M, N\in\mathcal{S}^n_o $.
Theorem 1.D Let $ K, L\in \mathcal{S}^n_o $ and $ p\geq1 $. If for any $ Q\in\mathcal{S}^n_o $, $ \widetilde{V}_{-p}(K, Q)\leq \widetilde{V}_{-p}(L, Q) $, then
with equality if and only if $ \Gamma_p K = \Gamma_p L $, here $ \Gamma_p^\ast M $ denotes the polar of $ \Gamma_p M $.
Ludwig (see [16]) introduced a function $ \varphi_\tau :\mathbb{R}\rightarrow[0, +\infty) $ given by $ \varphi_\tau(t) = |t|+\tau t $ for $ \tau\in[-1, 1] $. Using this function, Ludwig [16] defined general $ L_p $-projection bodies as follows: for $ K\in\mathcal{K}_o^n $, $ p\geq1 $ and $ \tau\in[-1, 1] $, general $ L_p $-projection body, $ \Pi_p^\tau K\in\mathcal{K}_o^n $, of $ K $ with support function by
where
and $ \alpha_{n, p} $ satisfies (1.4). For every $ \tau\in[-1, 1] $, the normalization is chosen such that $ \Pi_p^\tau B = B $. Clearly, if $ \tau = 0 $, then $ \Pi_p^\tau K = \Pi_p^0 K = \Pi_pK $.
Regarding general $ L_p $-projection bodies, Wang and Wan (see [17]) studied the Shephard type problem. Wang and Feng (see [18]) established general $ L_p $-Petty affine projection inequality. Wang and Wang (see [19]) gave the extremums of quermassintegrals and dual quermassintegrals for general $ L_p $-projection bodies and their polar.
Subsequently, according to definition (1.1) of $ L_p $-centroid bodies, Feng, Wang and Lu (see [20]) imported the notion of general $ L_p $-centroid bodies. For $ K\in\mathcal{S} _o^n $, $ p\geq1 $ and $ \tau\in[-1, 1] $, the general $ L_p $-centroid body, $ \Gamma_p^\tau K\in\mathcal{K}_o^n $, of $ K $ which support function is defined by
and $ c_{n, p} $ satisfies (1.2). The normalization is chosen such that $ \Gamma_p^\tau B = B $ for every $ \tau\in[-1, 1] $, and $ \Gamma_p^0K = \Gamma_pK $.
From the definition of $ L_p $-projection body, Wang and Leng (see [21]) gave the following concept of $ L_p $-mixed projection body. For each $ K\in\mathcal{K}^n_o $, real $ p\geq1 $ and $ i = 0, 1, \cdots, n-1 $, the $ L_p $-mixed projection body, $ \Pi_{p, i}K $, of $ K $ is an origin-symmetric convex body, which support function is defined by
for any $ u\in S^{n-1} $, the positive Borel measure $ S_{p, i}(K, \cdot) $ on $ S^{n-1} $ is absolutely continuous with respect to $ S_i(K, \cdot) $, and has the Radon-Nikodym derivative
By definitions (1.9) and (1.3), we easily know that $ \Pi_{p, 0}K = \Pi_p K $.
Just as the definition of the $ L_p $-mixed projection body, $ L_p $-mixed centroid body was introduced by Wang, Leng and Lu (see [11]). If $ K\subset\mathbb{R}^n $ is compact star-shaped about the origin, $ p\geq1 $, $ i\in\mathbb{\mathbb{R}} $, then the $ L_p $-mixed centroid body, $ \Gamma_{p, i}K $, of $ K $ is the origin-symmetric convex body whose support function is given by
for every $ u\in S^{n-1}. $ From this and definition (1.1), we have $ \Gamma_{p, 0}K = \Gamma_p K. $
For the studies of $ L_p $-mixed projection bodies and $ L_p $-mixed centroid bodies, Wang and Leng [21] demonstrated the Petty projection inequality for $ L_p $-mixed projection bodies, and then, Wang, Leng and Lu [11] obtained the forms of quermassintegrals and dual quermassintegrals of Theorem 1.A and Theorem 1.B. Moreover, on one hand, associated with the definition of quermassintegrals, Wang and Leng [10] extended Theorem 1.C to the quermassintegrals; on the other hand, Wang, Lu and Leng [13] gave the dual quermassintegrals form for Theorem 1.D. In regard to the studies of the $ L_p $-mixed projection bodies and the $ L_p $-mixed centroid bodies, see also [22-25].
According to definitions (1.5) and (1.9), general $ L_p $-mixed projection bodies were raised by Wan and Wang [26]. For $ K\in\mathcal{K}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $ and $ i = 0, 1, \cdots, n-1 $, the general $ L_p $-mixed projection bodies, $ \Pi_{p, i}^\tau K\in\mathcal{K}_o^n $, whose support function is provided by
From (1.11) and (1.5), if $ i = 0 $, then $ \Pi_{p, 0}^\tau K = \Pi_p^\tau K $.
Similar to Wan and Wang's idea, we define general $ L_p $-mixed centroid bodies as follows: for $ K\in\mathcal{S}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $ and $ i $ is any real, the general $ L_p $-mixed centroid body, $ \Gamma_{p, i}^\tau K\in\mathcal{K}_o^n $, of $ K $ is presented by
where $ \gamma_{n, p}(\tau) $ is the same as (1.8). Especially, if $ i = 0 $, by definitions (1.12) and (1.7), we easily get $ \Gamma_{p, 0}^\tau K = \Gamma_p^\tau K $.
In this article, we first extend Theorem 1.A and Theorem 1.B to quermassintegrals and dual quermassintegrals, which can be stated as follows.
Theorem 1.1 Let $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $ and $ i, j = 0, 1, \cdots, n-1 $. If for any $ Q\in\mathcal{K}_o^n $,
then
Equality holds in (1.13) for $ p = 1 $ if and only if $ \Pi_{p, j}^\tau K $ and $ \Pi_{p, j}^\tau L $ are translates; for $ p > 1 $ if and only if $ \Pi_{p, j}^\tau K = \Pi_{p, j}^\tau L $. Here $ W_{p, j}(M, N) $ $ (j = 0, 1, \cdots, n-1) $ denotes the $ L_p $-mixed quermassintegrals of $ M, N\in\mathcal{K}_o^n $.
Theorem 1.2 Let $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $, real $ i\neq n $ and $ j = 0, 1, \cdots, n-1 $. If for any $ Q\in \mathcal{K}_o^n $,
then for $ i<n $,
for $ n<i<n+p $ or $ i>n+p $,
Equality holds in (1.14) or (1.15) for $ i\neq n+p $ if and only if $ \Pi_{p, j}^\tau K = \Pi_{p, j}^\tau L $. For $ i = n+p $, inequality (1.15) is identic.
Moreover, we establish the following inequalities of quermassintegrals and dual quermassintegrals for general $ L_p $-mixed centroid bodies, which is regarded as a generalization of Theorem 1.C and Theorem 1.D.
Theorem 1.3 Let $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $, real $ i\neq n $ and $ j = 0, 1, \cdots, n-1 $. If for any $ Q\in \mathcal{S}_o^n $,
Equality holds in (1.16) for $ p = 1 $ if and only if $ \Gamma_{p, i}^\tau K $ and $ \Gamma_{p, i}^\tau L $ are translates, for $ p>1 $ if and only if $ \Gamma_{p, i}^\tau K = \Gamma_{p, i}^\tau L $. Here $ \widetilde{W}_{-p, j}(M, N) $ $ (j\neq n) $ denotes the $ L_p $-dual mixed quermassintegrals of $ M, N\in\mathcal{S}_o^n $.
Theorem 1.4 Let $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $, real $ i, j\neq n $. If for any $ Q\in\mathcal{S}^n_o $,
Equality holds in (1.17) for $ j\neq n+p $ if and only if $ \Gamma_{p, i}^\tau K = \Gamma_{p, i}^\tau L $. For $ j = n+p $, inequality (1.17) is identic.
Obviously, taking $ i = j = \tau = 0 $ in Theorems 1.1–1.4, then inequalities (1.13)–(1.17) reduce to Theorems 1.A–1.D, respectively.
This paper is organized as follows. In section 2, we provide some basic notions and results. Section 3 gives the proofs of Theorems 1.1–1.4.
If $ K $ is a compact star-shaped (about the origin) set in $ \mathbb{R}^n, $ then its radial function, $ \rho_K = \rho(K, \cdot):\mathbb{R}^n\setminus\{0\}\longrightarrow[0, +\infty), $ is defined by (see [2])
If $ \rho_K $ is positive and continuous, then $ K $ is viewed as a star body (about the origin). Two star bodies $ K $ and $ L $ will be dilates (of one another) if $ \rho_K(u)/\rho_L(u) $ is independent of $ u\in S^{n-1}. $
If $ K $ is a nonempty subset of $ \mathbb{R}^n $, then the polar set $ K^\ast $ of $ K $ is defined by (see [1, 2])
If $ K\in\mathcal{K}_o^n, $ it follows that $ (K^{\ast})^\ast = K $ and
For $ K, L\in\mathcal{K}_o^n $, real $ p\geq1 $ and $ \lambda, \mu\geq0 $ (not both zero), the $ L_p $-Minkowski combination (also called the Firey $ L_p $-combination), $ \lambda\cdot K+_p\mu\cdot L\in\mathcal{K}_o^n $, of $ K $ and $ L $ is defined by (see [27])
where the operation $ \lambda\cdot K $ denotes Firey scalar multiplication. Obviously, Firey scalar multiplication and usual scalar multiplication are related by $ \lambda\cdot K = \lambda^{\frac{1}{p}}K $.
For $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, $ \lambda, \mu\geq0 $ (not both zero), the $ L_p $-harmonic radial combination, $ \lambda\star K+_{-p}\mu\star L\in\mathcal{S}_o^n $, of $ K $ and $ L $ is defined by (see [28])
Here $ \lambda\star K $ denotes $ L_p $-harmonic radial scalar multiplication, and we can see $ \lambda\star K = \lambda^{-\frac{1}{p}}K. $ Note that for convex bodies, the $ L_p $-harmonic radial combination was investigated by Firey (see [29]).
If $ K\in\mathcal{K}^n $, the quermassintegrals $ W_i(K) $ $ (i = 0, 1, \cdots, n-1) $ of $ K $ are defined by (see [1, 2])
where $ S_i(K, \cdot) $ $ (i = 0, 1, \cdots, n-1) $ is the mixed surface area measure of $ K\in\mathcal{K}^n $, $ S_0(K, \cdot) $ is the surface area measure of $ K $. In particular, we easily see that
In [30], Lutwak defined the $ L_p $-mixed quermassintegrals and showed that for $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $ and $ i = 0, 1, \cdots, n-1 $, the $ L_p $-mixed quermassintegrals $ W_{p, i}(K, L) $ has the following integral representation
Here $ S_{p, i}(K, \cdot) $ $ (i = 0, 1, \cdots, n-1) $ satisfies (1.10). The case $ i = 0 $, $ S_{p, 0}(K, \cdot) $ is just the $ L_p $-surface area measure $ S_p(K, \cdot) $ of $ K\in\mathcal{K}_o^n. $
From (2.2), (2.4) and (1.10), it follows immediately that for each $ K\in\mathcal{K}_o^n $ and $ p\geq1 $,
For the $ L_p $-mixed quermassintegrals $ W_{p, i}(K, L) $, Lutwak [30] established the following Minkowski inequality
Theorem 2.A If $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $ and $ i = 0, 1, \cdots, n-1 $, then
with equality for $ p = 1 $ if and only if $ K $ and $ L $ are homothetic, for $ p>1 $ if and only if $ K $ and $ L $ are dilates.
For $ K\in\mathcal{S}^n_o $ and real $ i $, the dual quermassintegrals, $ \widetilde{W}_i(K) $, of $ K $ are defined by (see [31])
Obviously,
In 2005, Wang and Leng [32] introduced the $ L_p $-dual mixed quermassintegrals as follows: for $ K, L\in\mathcal{S}^n_o $, $ p\geq1 $ and real $ i\neq n $, the $ L_p $-dual mixed quermassintegrals, $ \widetilde{W}_{-p, i}(K, L) $, of $ K $ and $ L $ are given by
From formula (2.9) and definition (2.7), we get
For the $ L_p $-dual mixed quermassintegrals, Wang and Leng (see [32]) proved the following Minkowski inequality.
Theorem 2.B If $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, real $ i\neq n $, then for $ i<n $ or $ n<i<n+p $,
for $ i>n+p $,
Equality holds in each inequality if and only if $ K $ and $ L $ are dilates.
In this section, we prove Theorems 1.1–1.4. First, the following lemmas are necessary.
Lemma 3.1 If $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $ and $ i, j = 0, 1, \cdots, n-1 $, then
Proof According to definitions (2.4) and (1.11), and using Fubini theorem, we get
Lemma 3.2 If $ K\in\mathcal{K}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $, real $ i\neq n $ and $ j = 0, 1, \cdots, n-1 $, then for any $ M\in\mathcal{S}_o^n $,
Proof From definitions (2.4), (2.9) and (1.12), and using $ nc_{n-2, p} = (n+p)c_{n, p} $, we have
Lemma 3.3 If $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, $ \tau\in[-1, 1] $ and reals $ i, j\neq n $, then
Proof Due to considerations (2.9), (1.12), (2.1) and Fubini theorem, we obtain
Proof of Theorem 1.1 Since $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $, $ j = 0, 1, \cdots, n-1 $, and for any $ Q\in\mathcal{K}_o^n $,
thus for any $ M\in\mathcal{K}_o^n $, let $ Q = \Pi_{p, i}^\tau M $, where $ \tau\in[-1, 1] $ and $ i = 0, 1, \cdots, n-1 $, then (3.4) gives
By (3.1), we see that (3.5) can be written as the following inequality
Taking $ M = \Pi_{p, j}^\tau L $ in (3.6), and using (2.5) and inequality (2.6), we get
namely,
Notice that $ 0\leq i<n $ and $ p\geq1 $, then inequality (3.7) can be expressed by
this is just inequality (1.13).
According to the equality conditions of inequality (2.6), we see that equality holds in inequality (1.13) for $ p = 1 $ if and only if $ \Pi_{p, j}^\tau K $ and $ \Pi_{p, j}^\tau L $ are translates, for $ p>1 $ if and only if $ \Pi_{p, j}^\tau K = \Pi_{p, j}^\tau L $.
Proof of Theorem 1.2 For $ K, L\in\mathcal{K}_o^n $, $ p\geq1 $, $ j = 0, 1, \cdots, n-1 $, and for any $ Q\in\mathcal{K}_o^n $,
so, let $ Q = \Gamma_{p, i}^\tau M $ for any $ M\in\mathcal{S}_o^n $, where $ \tau\in[-1, 1] $ and real $ i\neq n, n+p $. We get
From (3.2), we know that
For $ i<n $ or $ n<i<n+p $, taking $ M = \Pi_{p, j}^{\tau, \ast}L $ in inequality (3.8), and using (2.10) and inequality (2.11), we obtain that
that is
Therefore, for $ i<n $, inequality (3.9) has the following simple form
this yields inequality (1.14); for $ n<i<n+p $, inequality (3.9) shows
i.e., inequality (1.15) is obtained.
Similarly, for $ i>n+p $, taking $ M = \Pi_{p, j}^{\tau, \ast}K $ in (3.8), and utilizing (2.10) and inequality (2.12), we easily obtain that
notice that $ i>n+p $, we get inequality (1.15).
According to equality conditions of inequalities (2.11) and (2.12), we know that for $ i\neq n+p $, equality holds in (1.14) or (1.15) if and only if $ \Pi_{p, j}^{\tau, \ast}K = \Pi_{p, j}^{\tau, \ast}L $, i.e., $ \Pi_{p, j}^{\tau}K = \Pi_{p, j}^{\tau}L $. For $ i = n+p $, by (3.8) and (2.9) we know that inequality (1.15) still holds.
Proof of Theorem 1.3 For $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, real $ i\neq n $ and any $ Q\in\mathcal{S}_o^n $, since $ \widetilde{W}_{-p, i}(K, Q)\leq\widetilde{W}_{-p, i}(L, Q) $, therefore, for any $ M\in\mathcal{K}_o^n $, $ \tau\in[-1, 1] $ and $ j = 0, 1, \cdots, n-1 $, let $ Q = \Pi_{p, j}^{\tau, \ast}M $, we get
Together with (3.2), we obtain
Taking $ M = \Gamma_{p, i}^\tau L $ in inequality (3.10), and using (2.4) and inequality (2.6), we have
this is just inequality (1.16).
According to the condition of equality in (2.6), we know that equality holds in inequality (1.16) for $ p = 1 $ if and only if $ \Gamma_{p, i}^\tau K $ and $ \Gamma_{p, i}^\tau L $ are translates, for $ p>1 $ if and only if $ \Gamma_{p, i}^\tau K = \Gamma_{p, i}^\tau L $.
Proof of Theorem 1.4 For $ K, L\in\mathcal{S}_o^n $, $ p\geq1 $, real $ i\neq n $ and any $ Q\in\mathcal{S}_o^n $, because $ \widetilde{W}_{-p, i}(K, Q)\leq \widetilde{W}_{-p, i}(L, Q) $, thus let $ Q = \Gamma_{p, j}^{\tau, \ast}M $ for any $ M\in\mathcal{S}_o^n $, where $ \tau\in[-1, 1] $ and real $ j\neq n $, then
From (3.3), we get
For $ j<n $ or $ n<j<n+p $, taking $ M = \Gamma_{p, i}^{\tau, \ast}L $ in (3.11), and together with inequality (2.11), we have
i.e.,
This is inequality (1.17).
For $ j>n+p $, let $ M = \Gamma_{p, i}^{\tau, \ast}K $ in (3.11), and together with inequality (2.12), we have
this yields inequality (1.17).
According to equality conditions of inequalities (2.11) and (2.12), we see that for $ j\neq n+p $, equality holds in (1.17) if and only if $ \Gamma_{p, i}^{\tau, \ast}K = \Gamma_{p, i}^{\tau, \ast}L $, i.e., $ \Gamma_{p, i}^{\tau}K = \Gamma_{p, i}^{\tau}L $. For $ j = n+p $, by (3.11) and (2.9), we see that inequality (1.17) is still true.